my recommendation would be to go for a 35mm 1.4L as that will turn out ot be a great walk around lens when you decide to go FF. The 24mm has alot of picture quality issues compared to the 35mm from what i've read from http://www.photozone.de/canon-eos/152-canon-ef-24mm-f14-usm-l-test-report--review
I myself am stuck in a similiar situation of whether to get more glass or a new body (i having the 550d means i have the same AF as the 5d mk2 it seems)
Since all you have is the 50mm prime the biggest limiter you have right now is lack of a wide lens and a zoom lens. My thinking is that there is alot of camera equipement that i still don't have, so i'm going to concentrate on getting a flash, a good zoom, nd filters and such before i get a better camera. As those will help with my actual photography skills while upgrading my body not so much.
A friend once gave me this sound advice "you should only upgrade your body once your photography starts to become limited by it. I upgraded because the AF was horrible and the camera kept having problems and wasn't reliable for concert photography".
One other thing that has been said on the forums, it is better to have a L glass on a rebel (500d series) than to have a kit lens on a pro body.