The Xti is an interesting case, since the 400plus firmware hack gives it unbelievably more power. I hung on to my Xti for another 2-3 years just because of that.
The 30D is a great camera - no firmware hacks, however to give it a boost.
It depends on the type of photography you want to do. While I skipped over the 30D myself I did have the 20D which is extremely similar. I found I was missing shots of sports due to relatively low burst speed, and low light performance was poor beyond ISO 400 (sometimes pushed to 800).
I upgraded to a 60D last year, much better burst speed, but more importantly for me I can comfortably shoot at ISOs above 2000 with no issues.
I'd agree with GeoffSobering above - keep that 30 for a while and see what you need to get the shots you want.
All I've really figured out with 400plus is the shutter count (which is under 9k. For owning it 6 years, that's not much, I gotta step it up!). I need to immerse myself in the user guide one of these days. I do wish I had better high iso performance but I can live. I do need to get noise ninja or something similar in the meantime, though.
I do feel self conscious trying to shove it in my purse and bring it out while doing normal day to day stuff. And it's too big to put in my backpack and bring to campus with me. So instead of buying a new body, I bought a used fuji x100 off amazon yesterday. It should have better high iso capabilities than the xti and honestly I mainly shoot indoors for casual social stuff and I feel like the x100 won't stand out so much in those cases. Plus I can use it as a nice point and shoot when I don't have the room for my xti. I think it'll be more useful for me than a new dslr body for a while, since in the last three years or so I've taken my xti out with me maaaaybe three times? So I think it'll be a nice compliment to the xti and an upgrade stepping stone.