I'm assuming you're talking about owning 2 TW's?
I certainly wouldn't "upgrade" from a 2001 to a 2008, unless yours is in extremely bad condition. They are the exact same bike, except for paint/stickers, and if you've got my luck, the 2008 will have the infamous 2005-2008 leaking base gasket problem.
If you're wanting to add a TW to your stable, my rule of thumb is to get a brand new one if you're within $1000 of the price of a new one. In my area, I can get a new one out the door for $3700. Of course, I would probably make an exception if I was absolutely sure, beyond a shadow of a doubt, that the 2008 was "perfect". As qwerty implied, there are better deals out there if you're willing to spend some time looking.