I'm with the others who are telling you to get the 17-55 f/2.8 IS over the 24-70L based on current need.
I, like you didn't want to buy crop glass for a long time... but for a different reason than you... I still shoot film and wanted as much of my kit to work on both platforms as possible. That is UNTIL I finally rented the 17-55 f/2.8 for a week for an event I had been asked to shoot. I ended up buying one a few months later. Its a wonderful piece of glass. Sure there is the occasional zoom creep, sure its not built like an L. But its as sharp as an L, the colors come out spectacular, the focus is f***ing fast, and the IS is a BIG helper. And once I added a filter to the front... its pretty much ready to face the elements.
Be aware that if you go with the 24-70L you're not getting much wider than your 28-75 f/2.8 (which according to most reports is a wonderful lens, I've never used one, but I'll take the majority's word for it), but it is A LOT more expensive and A LOT heavier. The 17-55 f/2.8 IS USM gives you a USABLE wide-end for your walk-around lens. Then sell the 28-75 f/2.8 eventually and use the money along with what you saved by getting the 17-55 over the 24-70L and pick up the Tokina 11-16 f/2.8. That way you have a REAL UWA-Normal coverage @ f/2.8 with sharp solid glass.
When you upgrade to FF, whether its 1.5, 2, or 5 years, there will be a 2nd-ary market for the glass to unload. And to be fair, the 11-16 f/2.8 is used by many on 1.3x and FF @ differing focal ranges to great effect without vignetting (on APS-H (1.3x) it can be used from 12.5-16mm, on FF it can be used from 14-16mm... you can use the lens all the way down to 11mm on each without fear of mirror collision but be ready to do some cropping). People even opt to use the lens ALONG with the 16-35 f/2.8 MkII on FF and APS-H. But for APS-C its a no-brainer.
Honestly, since getting my 7D, almost all want for an APS-H or FF body has gone away. This camera works incredibly. The AreaAF is reminiscent, yet much better, than the implementation in my EOS-3. the AF locks faster and much more accurately with all my lenses right out of the box... I have yet to play with MLA, but simply haven't seen the need... its just THAT good. The 8fps is such a big jump from the 40D's 6.5fps especially when shooting sports and firing thru an entire action sequence (pitcher's motion, tennis swing, golf swing)... the 2 frames you get help a lot. But the camera isn't as weather sealed as a 1D3 or 1D4 or 1Ds3 (or the upcoming 1Ds4) - and if you're concerned about your lenses and the elements, you should be aware that any system is as good as its weakest link, and in your case it would be the 7D. So you expect to shoot in gale-force wind and hurricane rain conditions, buy some environmental protection for your gear - I got a KATA rain-hood for my 7D+70-200 f/4L IS for World Series Game 1 when rain was expected... I ended up shooting the whole night with that contraption.
Get the right gear now, for what you need now.