OP, this is a very loaded question and should raise some interesting debates. It's a good one though!

The way I see it, high-end appliances deliver a few things, most of which are completely subjective:

A specific design/aesthetic. It is tough to get industrial or elegant design in an $800 appliance.

Cooking flexibility - a $2000+ GE Profile range may have double ovens, an integrated meat thermometer, 5th burner with griddle, warming drawer, high output burner(s), e.g. 15k plus BTU, convection, dual convection, better interior lighting...

And on and on. Basically the buyer has to decide if any of those items are worthwhile and, how much are they worth to them?

On one hand, what you have now works great and does all you need. But the same could be said for cars - my Honda Civic gets me to work and back but my Acura TL does the same with more comfort, features, better sound, and so forth. What I mean to say is, you don't know what you don't know. If you have used the above "features" and do not need them or feel they will improve your process, then they likely aren't worth it for you.

I cannot speak to dishwashers, we have a stainless Kitchen-Aid and at 8 years old it's been a workhorse champ, 0 issues.

I hope this is of some help!

toddrhodes wrote a great post --- this certainly is very subjective and there are a lot of opinions. And, people cook great meals on camp stoves.

On dishwashers, I believe it is possible to buy too low. You end up lacking in cleaning performance and sacrificing in reliability. For a relatively small amount of money, you can step up a price class or too and get a DW that is more efficient, does a better job cleaning, and is more reliable. Stepping up from a $300 to $600 machine gives you a lot more tangible benefits than say, stepping up from a $900 DW to an $1800 DW.

Are you asking for which features are most important? it is a bit subjective but I'm certain the appliance experts here could give you some concrete examples.

I agree that there is a lot of subjective preference as well as some features or design aspects that that may --- or may not -- matter. There are also a lot of differing opinions on what are "high end" appliances.

A search here will turn up threads with debates over topics like "Are Subzero refrigerators s worth it?"

Here's my 2 pennies worth on this debate.

Why spend $1800 for a gas range instead of $800? :

To start with, more money can get you an induction range if you can work with electric ranges. Induction has the controllabilty and quick response of gas with potentially less kitchen hassle and maybe less worries with the little ones messing with the stove.

Also, more money also can get you a "dual fuel" range which means gas burners over top of an electric oven. Some people prefer electric ovens to gas and vice versa.

My experience has been that it generally gas verus electric ovens in this price range is not a big deal in terms of cooking performance. A a gas oven puts more heat into your kitchen, though.

Also, in the $1800 price range, numbers of the dual fuel ranges will have a third element that wraps the convection fan and that can help with more even baking (with less fussing with trays) when baking, say, mass quantities of cookies.

Since you said you are looking for a gas range, I'm guessing that your kitchen does not have the 240v connection you'd need for induction or dual fuel stoves.

If memory serves, I think there is a Frigidaire gas range which has an electric "third element" convection set-up in the gas oven. I've seen it discussed here but don't remember any specifics. Might be worth checking out.

More money for a gas range also can get you a range with two separate oven compartments. The smaller ovens heat up faster and allow you to bake or roast two things at different temps.

Numbers of gas ranges in the $1500 to $1800 price range have electric warming drawers. Some folks find them useful, others not so much. The warming drawer was a selling point for me when I bought my previous range, a GE dual fuel model, back around the turn of the century. I found that it took so long to heat up that it was not much of a convenience for me and I rarely used it. Others here are very happy with their range-bottom warming drawers and use them constantly.

More money also gets you a better choice of burners, but the importance of this factor is a function of personal preferences and the cookware you use and what you cook in it. If you like to stir fry/saute in 12" skillets, you will likely find it easier to do so with the bigger burners on the more expensive stoves, some of which have multiple rings of burner jets. Some find these useful for boiling water quickly for pasta, oatmeal and etc. for the impatient little ones.

Also, many mid-range (and above) gas stoves can be had with a central burner for a pancake griddle. Some find the griddles useful because the central burner makes for more even heating than you get by straddling a large and small burner with a griddle plate.

Also, as you move into mid-rage and above, you'll find continuous grates (easier to move pots around) and slide-in style of ranges (all controls down front, so no reaching over hot pans to adjust the oven)

Gas stoves in the mid-range and above may have larger ovens than less expensive ranges. Also, as you get over the $1500 price mark, electric warming drawers become common. Some find those useful and others do not.

Then there are the "pro-style" ranges or pro-look ranges such as (I believe) a stainless finished GE Profile for around $1900. AFAIK, the only one at or below $1800 is the NXR from Costco. The selling point for the NXR is that it has four larger "dual stacked" topside burners at 15k btu which give good flame-spread from high heat to a ridiculously low simmer with the extra real estate of the pro-style construction. This will be useful if you find you regularly cook with three and four large pots at once, or you want to use a 14 x 23 pancake griddle like the Chef King or Vollrath. If you tend to cook with smaller pans (say 8-inch nonstick frypans and small saucepans) this will not be so useful.

A basic type of pro-style stove like the NXR will have relatively minimal electronics, so theoretically less to break and easier to fix when something wears out. You might (or might not) find them easier to keep clean. The stainless steel top is probably easier to keep clean than the black enameled tops of most gas stoves in this price range, but it does not have a self-cleaning oven.

So, think about your budget and your priorities.

More money for dishwashers :

The recent DW testing by Consumer Reports concluded that just about everything now being sold, even the junkers, will do a perfectly acceptable job of cleaning dishes.

As you move up in price, you get a number of things that may be of varying importance such as:

(a) faster cycles. The bottom of the line DW may take 3 hours to run and dry a load. A higher level model may have cycle times less than half that. A big deal when doing lots of dishes and maybe worth your while.

(b) Quieter operation. Some of the better brands will be dramatically quieter than the least expensive models. Quieter operation may be a big deal in a small house when trying to get little ones to sleep or when having discussions at the dinner or kitchen table.

(c) stainless steel interiors. A big deal for the DWs that do not use heated dry (which, btw, are much more plastic-friendly than heated dry models). Stainless tubs also tend not to show wear as quickly as the tubs made of synthetic materials.

(d) conveniences like flatware racks instead of baskets. (Some wouldn't have a DW withouth flatware racks but others, like me, prefer baskets.)

(e) More cycle options. Some folks find these very useful, others not so much. (For example, I don't own any fine crystal glassware so a cycle for crystal is not something I would use,)

(f) hidden control panels and/or the ability to take paneling to match cabinetry. (Important to some and unimportant to others.)

(g) more flexibility with rack and tine arrangements.

I went with a mix of high end and mid range, everything better than anything I've ever had before. For me a 48 inch r/f was very important and sz had the one I liked the best. I am in love with this fridge.

Range/oven/cook top:
From what I have read here, few die hard "cooks" would sacrifice at all on their ovens. Very few regrets posted on any of the high end ovens, most regret not spending a bit more for their dream oven.

I upgraded from a basic 20 year old non-convection electric 20 Amana range that was an 80s eyesore but cooked OK and was still working when we parted ways. But I cannot understate how much better a modern $800 convection KitchenAid range cooks in comparison. Electronic timers, appearance, reduced cook times, even heating, easy clean glass cook top. Worth every dime. I did not look at over $1000 ranges, but I wish I would have based on what I have read here after the fact.

Dishwashers
I got a bottom of the line Miele Futura Classic 4225 dishwasher for $900. I don't use crystal and china much, but if you don't mind just spartan cycle choices like pots and pans, normal, economy, sanitize wash, and rinse and hold, it delivers great value. It's smaller on the inside than my old GE Profile dishwasher, but holds plates, cereal bowls, serving bowls, glassware, and utensils more efficiently and is quiet enough at 47 dB to work in my open concept layout.

Miele does require a separate outlet and the outlet hose at 7/8 can pose issues for code-installs as the only dishwasher siphon breaks I find are for 5/8 hose. Having had a plastic interior before I would highly endorse the stainless interiors for long term ease of cleaning which is standard on all Miele. Some have noted limited service areas with Miele, and dealerships are few and far between.

Best of luck.