The way I understand things, hard water is bad, because it leaves deposits. Contaminated water is bad, because the contaminants can clog things. Demineralized water (distilled or reverse-osmosis) is bad, because complete lack of minerals makes water more prone to corroding metals. And acidic or alkaline water is similarly bad. So, ideally, you supply soft clean tap water. Where that isn't available, an ion-exchange water softener can remove hardness without removing total amount of minerals. And a carbon or particle filter can remove contaminants, if applicable. These restrictions are true for all kitchen appliances regardless of brand. So, switching from Miele to Wolf just because the wording in their manual is different doesn't actually buy you more reliability. Switching from plumbed to supplying suitable (!) bottled water would help though. And you can do that with either brand. And installing appropriate point-of-use water treatment would work just as well.

I went through the same question some years back. Miele has more features for the $$, so I originally wanted that, but at the time they didn't have a combi/convection steam oven that could take 208V (what I had), so I settled with the Wolf instead. And I must say, I've been really happy with it. It works, it's not fussy. Yes, it doesn't have the color swipey screen the Miele has, but I'm not convinced I miss that all that much. Would I like a broiler? I think so, as it is something I use, but I do have another big oven with the broiler (that unit almost always takes a backseat to the convection steam unit) and I can use that when I'm broiling something, so it's not too bad. I've kept tabs on the Miele, and I've discovered that considering that if you don't get a plumbed unit, the Wolf is more forgiving than the Miele on how much water is in the tank (I'm pretty lazy and never fill it up all the way, and the Wolf lets me still use it as long as I have enough water). If you really want to go into the details about adjusting settings, moisture level, turning on upper element broiler, you'll want the Miele, but if you just want to use it, I think you'd like the Wolf. I certainly don't regret having to "settle" for it at all.

You'll see a lot of me in that 2008-14 group. :) And, yes, the lines have changed a lot. I dove back in a couple of years ago when I was helping several people and more up on the new things, but that's why I nearly ducked out when I remembered the "grills", but stayed in on the basis of getting the ball rolling. Given the range and the guaranteed CSO, you've sported an easier to answer question. If you're mostly using your Advantium as a convection oven or microwave, rather than a speed oven, you may not need one. There's no guaranty, even, that you will like a new Advantium as well as the one you've been using. Nothing replaces a speed oven if you're using the speed settings. I rarely do, because my need for such changed at about the time I had it installed, but in a pinch there's nothing better than the Advantium. Moreso than other appliances trying to be speed ovens (I'm not counting the TurboChef, which is a can of worms floating in a kettle of fish). Kim's right about testing out the "grill", and other features that are important to you, at a Miele gallery if there's one reasonably close to you (like worth travelling a couple of hours to get to). My own experience with baking, as in cocktail pastries, is that the regular oven is better than any convection only oven, though one of the combined settings on the Advantium might be better than convection only. I've often baked them in the regular oven, then reheated in the Advantium or CSO, and either works well for that. The biggest issue is crisp and flaky without being dried out. A pan with sides helps, as does the fact that both retain the steam from the food. Your best bet, given no further information, is to set up your new kitchen so that there's a space for an Advantium, with the correct electrical service available, since that's best done while you have the whole thing open. Have a cabinet that can accommodate it without further carpentry then removing the doors and adding a trim frame (maybe get the trim now. Or put a standard microwave there and just get some extra trim. That way, you're inoculated. If you're pining for the Advantium later, it won't be prohibitive to put it in. In general, however, unless you're planning those overly big dinner parties, you don't need three ovens, and if you're not using Speed, you only need a microwave.

@Mr Kyle I'm also interested in your question. In my home we have a non Miele 30" convection oven and a 24" Miele CSO. We end up using the Miele CSO for most cooking because it's more energy efficient with the use of space and does most everything the CO does and more. We end up using the larger 30" oven (without steam injection) for when we want to do homemade Neapolitan pizzas on a pizza steel, and for baking two sourdough loaves at a time (crockpot method or wetted mixing bowl on top method), which is our typical use case. Essentially, it's used 10% of the time. We sometimes use the MagicChef settings when we know what's going on with time, temperature, and humidity level for each step. Miele seems to have done away with sharing that information in recent ovens that have MagicChef Plus, so we would be less inclined to get something new from them.