I wouldn't mind seeing a tiny bump in screen real estate, but I don't want the phone to get any bigger. I've had large screen phones before and they aren't comfortable to use.
I have an iPad and use it often. If I want big, I've got it. For my phone, I want it to disappear in my pocket. I'd love it to be thinner, but more importantly lighter.
If the next generation looks great and the total height/width are the same, I'll consider it. If it has great new features, in addition, I'll definitely buy it. If they slap a 4"+ screen on it, I'll likely keep my 4S--unless there is some new feature I can't live without. I'll still gripe the whole time about the hugeness of it though.