BBQ's get grungy...baked-on grungy. Exteriors with lid closed can usually be kept somewhat presentable but otherwise forget it. The lid-open interior will simply get worse and worse. Nature of the beast. Wipe/scrape off what you can and otherwise don't worry about it. Some people think stainless is harder to "keep clean" than other surfaces. IMHO if "pretty" is what you want in a grill, your priorities are reversed. New grills are always pretty. Used grills never are.

When I'm invited to a BBQ-type party, one way I've learned to tell if the "chef" knows what he's doing or not is simply to look at the grill. If its wonderfully clean, I know they don't grill very much. If one does a lot of grilling, the device will look it no matter what its made of. Grilling is messy, smoky business. And there's nothing like it!

June 2006 issue of Consumer Reports has section on gas grills. On page 40 they have some comments specifically about SS.

My grill is usually a mess, but I use it 6 nights a week, I just love to cook outdoors. That doesn't mean that I can't put together a great pasta figolli, but nothing beats the taste of a grilled piece of salmon or a fine KC Strip steak on the grill. Hence my grill is always dirty. Once a week I clean the grates in my dishwasher, and use a wire brush on them just after they get warm, oil and cook. Nothing fancy.
But when I put out an invite, my table is always filled with guests. On the outside I use an orange cleaner with oil. Spray on and hose off, some of the grime stays, but any "drippins" get swept away. By the way I love my Jen-Air grill, it's going on it's fifth season and it just keeps cooking better each time-or maybe I'm just getting better-nope gotta be the grill.

There are a few factors you need to consider and one of them is where you live and the climate. If you live near a beach the humid salt air will destroy grills made of anything but the best quality SS like 12 gage 403. The cheap Chinese stainless grills will rust away so fast you will wonder what happened. The high heat acts as a catalyst to cause the low nickel stainless steel to rust quickly.

The next factor is do you like a clean grill? I cook on my current grill, a Firemagic brand grill at least twice a week. It is not easy to keep clean and about once every couple of months I give it a good though rough cleaning and it is a good 1/2 day process. I am in the process of moving to a new home and my Firemagic is built in to the island in my current home so it stays. I have just ordered a TEC grill because it has a self cleaning feature like a self cleaning oven and it has easily removable panels/heat shields that can be put in a dishwasher for cleaning after the self clean cycle has reduced the gunk to a white ash. It is also all infrared 100% but with low temperature ability and the burner is sealed off from the food by an infrared emitting glass barrier. They aren't cheap, but neither was the Firemagic. They are made of very high quality materials in the USA.

There is a typo in my post above. The SS should be 304 not 403.