Is it worth getting a FX5900 if I have a ti4600 with this computer?

Ok, my computer is a 2 year old p4 1.7. I have a GeForce 4600. I'm wondering
if it is worth buying the latest and greatest graphic card or not. All the
benchmarks I've seen show the card running on high end systems
(understandably) but that doesn't help me out. I don't want to spend another
1500 to 2000 on a new computer for at least another year or so but I'd like
to be able to play some of the newer games like SWG with at least some of
the settings higher than zero. Anyone running the card on an older system?
Is it worth the money to upgrade or should I just sit with what I have until
I can buy a whole new computer (again, in a year to two years)? Any thoughts
would be appreciated.

Thank you in advance,

mega