Bruce,
As much as I despise the current generation Summits, I do like these. I prefer the Platinum version with the stainless frame. You may have seen my post about one listed by me for $200, same 4 burners but with the stainless frame, also with smoker burner and rear infrared for rotisserie. He hasn’t gotten any action in almost three weeks. His looks to have been treated much rougher than the one by you. I have thought of offering him way less, but then there are some serious things to consider:
The big issue on these is the front of the firebox where the burners go in. Some report burn-through while a few have said their Summit has a stainless front. The other issues are the unusual burner crossovers and the special flavorizer bars that cover them. Both can be pricey and probably knock you out of the flip market if the existing ones must be replaced.
These seem to be really nice grills. My hunch is that even well restored, though, they would not command any more than $400. I think when you get to that price point people start looking hard at new grills (even if not as well made). I don’t think there are enough discriminating buyers willing to pay the price that would allow you to restore one with replacement parts and still make any money for your efforts. It could be a great keeper if you wanted one, though.