Look, there is no right answer to this. If you're Donald Trump (are you?) and have $$cash$$ to burn, then why the hell not?? GO for it!

On the other hand....Looking at your X....if it was me personally, there is NO way in hell I would drop my lease on a virtually new 2008 4.8i just to jump on the latest and greatest model. Your X5 looks SWEET and you've got what..15,000 miles on it? 20,000 tops? It's basically still new. And it will still out-gun 95% of all the SUVs on the road. Outside of the sporadic Cayenne Turbo or GTS variants, or the Infiniti FX50, you are still King of the road.

Another way to look at it: there will always be something faster and better that comes out RIGHT after you buy something. Same thing with computers. One year goes by, and you no longer have the fastest, best machine money can buy. You may not go broke if you keep substituting your PC/Mac every year. But you sure as hell will rack up serious debt if you keep swapping your vehicle every time a better one comes out.

If that was my 4.8i, I would ride out the lease and bide my time.