I own a 2008 GXP now and have owned two different C6 Corvettes. I also rented a 2010 V6 Camaro two years ago for a week. The only redeeming quality I remember the Camaro having was a stellar V6.
This really comes down to what you want because these cars couldn't be more different. Coming from a GXP your decision is going to be pretty easy in my eyes and here's why:
Camaro - much newer, more roomy, less engaging, a hard-to-see-out-of barge that will feel heavy as a tank and corner like one (yes, even though it's an SS) too but......when you drop the hammer that LS3 will pull much more violently (and sound better) than a stock-ish GXP (just make sure it's pointed straight first). I'm not even going to talk about how cheap the interior/dash was.
Solstice - nimble, tossable, much lighter, harsher, much smaller, lower, can put the top down, requires more attention to drive, can wind out the engine more without venturing into the "go to jail" zone (I have GMPP tune and still isn't very fast to me). The GXP is truly "Corvette-Lite".
Yes, I'm biased.
I owned an LS3 Vette and there are not too many occasions where you can truly unleash it on the the street and not go to jail. These things nowadays are so economy tuned that just putting around you would never know you had 430hp on tap (a tune will fix that). There is an old saying "It's more fun to drive a slow car fast than to drive a fast car slow". I can attest a certain amount of truth to that.
One extended test drive will tell you what you need to know. The thing I find most worrisome in your situation if you switch is how heavy and lethargic the Camaro will feel compared to the GXP (that and it is very hard to see out of). IMO that will be the one thing that could make you regret your decision a month later.
Good luck and let us know what you decide. I still like the Camaro and what it is doing for GM. I would own a ZL1 if I could afford one (while keeping the GXP). But owning a SS for 15K - 19K would be a steal.