With regard to the "should I upgrade" question, I've found this chart to be fairly useful. It shows the 9600GT as being 10 tiers above the 7600GS.
That said, this chart is actually part of a monthly feature TH does called "Best Video Cards for the Money." Their <$100 section suggests the 9600GSO, HD4670, and HD3650. The 9600GSO is a bit cheaper and is only one tier lower. It actually performs roughly equal with the GT at lower resolutions because it has more stream processors, from what I've read.
The HD4670 is about the same price as this 9600GT, but what may interest you is that it has an onboard soundcard with 7.1 LPCM support via HDMI. So if you've got an extra-fancy surround setup you could get Dolby TrueHD and DTS-HD signals without them getting downsampled by the S/PDIF passthrough. Not to mention it would save you a lot of cabling.
The HD3650 borders on a joke recommendation, but you really can't beat the price at $35, and according to the hierarchy table it's actually 3 tiers above your current card. So if you're on a *really* tight budget you might consider it. (Plus it comes with WoW. Edit: Apparently it's also silent! )