I'd like to add, i'm in a similar situation with my 30D and considering the 5D, but is it worth the extra £800 px?, I'd like to think so, but the only extra you're getting on the 5D is full frame and better noise control and 2mp extra resolution (is it 10mp?).
I'd always recommend investing your money in lenses as they tend to hold their value better than bodies, and obviously, buying the best lenses you can afford will give you better IQ.
So to answer my question, and hopefully yours, i don't think it's worth upgrading my body before i acquire the lenses i want.