It depends on what you want your sampler to do. There are a few new features in the Ultra line, but according to an Emu rep I met, there aren't a great deal of differences. But that might have been the Emu rep trying to make some people feel okay about their less than year old sampler. Beat Munging is one of the big differences, but if you don't care about it - so what. I don't think you can use the RFX-32 card, but I don't even know how useful it is.

But the real question is, why would you upgrade? If the hardware is doing the job - run with it, if not...then why not? And what alternatives are out there?