when you update over the air with wifi and upgrade betas then it does an upgrade and not a restore but you still have to keep updating and then downloading new itunes otherwise your phone refuses to sync with itunes and so far a few apps i found dont work properly on ios 5 beta and ones i use a lot but beta 6 will expire on the 29th September so it looks like we are coming to the end of the betas soon ish.
I would definitely like to see a larger screen, since I have gotten use to a 4.3 inch screen. But for AT&T subscribers 4G is likely not to happen, I don't know about Verizon subscribers. But it would be nice to have 4G LTE capability on all carrier versions.
I really love my white iPhone 4 16gb so if I upgrade I'm going to miss it. I wouldn't mind a bigger screen, but I don't want my phone any bigger. I like that it is small and thin. I also have so many cases for my 4 I hate the thought of having to start all over with that. But knowing me I will upgrade because I always want the newest thing out!!