For performance reasons and if your using Win XP the answer should be no.
If for Dx 10 support then the jury is still out. I've completed the Crysis game with a current Dx 10 card, Ms. VISTA, @ 16 X 10 medium graphics on 939 X2 3800+ and played a few levels on Win XP with Radeon 800 GTO @ 800 X 600 on AM2 3600+ low graphic setting. The GTO played pretty smooth at this setting and I honestly didn't think it looked too shabby.
The destructible environment and 3D environment are the big draw cards here, but every gamers view of what's good is subjective. So if you're tempted by eye candy then see if you get to see it played on a well configured Dx 10 platform first and compare with yours, before retiring what is still pretty useful hardware. If you can wait I'm sure there is better to come.
If you can afford the 8800 GT card and you have VISTA then there won't be any need to return to your current SLi set-up as this card will handle all current games at 1400 X 900 with ease.