In the almost 2 years you've had your MSI 9800GTX oc I see no reason for you to get a new card right now unless you plan on rendering Toy Story 3 in real time.
I agree with this. My MSI GeForce 8800GT OC is still serving me more than fine.
P.S. I've had two MSI cards. The one here, and an MSI GeForce 8600GTS OC.
The latter was bad, not because it was an 8600GTS (wasn't half bad actually), but because it had a "flaw" in it's design to where the fan always ran full speed unless paired with an MSI motherboard (had it paired with an ASUS first, then a Gigabyte), and the fan was ridiculously loud. I took it our of my then secondary PC, and it fell nearly silent. I put it back in, and it sounds louder than my primary PC with a nearly open case, many more fans, four hard drives, etc. (although my primary system isn't loud by any means, but still). Stuff like this is the stuff you research different brands for.