If you only use the PC to emulate, I believe that it is not necessary for now an update
Your CPU is not bad, but if you could do an Over Clock, would have a significant improvement... i think 3.0 GHz and you´re good to go. Emulators usually need more CPU than a GPU, of course if you use very high resolutions with filters etc., a 1GB GPU mid-end will be most suitable.
The most important thing in your situation, I think it's using the new SVN 251 and a 64Bit OS. Here i use W7 x64 Ultimate ... the difference in frames per second for supermodel 32bit to supermodel 64bit is approximately 8% 10% .. Daytona USA 2 on 32Bit at 55 fps, 64Bit at 60 fps constants.
cheers