I have two different answers for you...
1. If you're rich, sell it and buy a new one.
2. If you're not rich, KEEP IT!
I just went through the same thing you're going through. I have a bone stock '03 H2 with 76,000 miles on it. Was going to trade it in for a new '06 (GM is offering $6,500 cash back OR 0% financing for 72 months on those).
The stealership offered me $26,000 for mine. Once I crunched the numbers, I realized that if I were to by the new '06 H2 SUT I wanted (sticker was $63K), I'd have to leave that one bone stock because certain upgrades will void the warranty and I wouldn't have the $$$ to get any upgrades anyhow.
However, if I keep the one I have now, I can drop a brand spankin' new engine in the beast (as well as plenty of other things) for WAY less than a new one will cost me.
So, I'm gonna keep the one I have and I just placed a large order for a Fabtech 6" Lift, Fabtech Heavy Duty Tie Rods, Fabtech Steering Stabilizer, Fabtech Duel Shocks, 20" Moto Metal Rims, 38" Tires, H20 Rear Bumper, H20 Corner Ladder (X2), Black Door Handles (I hate chrome), and a Tilt Meter. And I've still got plenty of $$$ left over.
