I have been struggling with this exact same decision for the last 12 months. And I do mean struggling with it. I have finally chosen to purchase the 17-55. The reason I haven't done this sooner was I was waiting to see if the 24-70 with IS would come out soon and what the price will be. However, Canon has been raising prices on new lenses significantly. For example look at the 70-200 f/2.8L IS II - big jump. I would expect the same for a new 24-70.
I actually rented both lenses from LensRental.com at the same time. I soooo much wanted to love the 24-70 more than the 17-55, because it was an L lens - and I really wanted an L lens. At the end of the day, I took much better pictures with the 17-55. I determined it was largely due to the IS, and at that point I decided I wouldn't purchase a lens without IS (hence waiting for the new 24-70 w/ IS). Also, the 17-55 was much lighter and smaller on the camera. I felt like I was carrying around a brick with the 24-70 - so for casual everyday indoor use - that was going to get old after a while. So as much as I wanted to like the 24-70 more, I had to be honest and admit it wasn't even close - the 17-55 was better for me. (I also rented the 24-105 F/4L IS and I liked that better then the 24-70 as well - better range, has IS and it is just 1 stop slower).
Other considerations - The ISO on your camera body. Honestly, I don't think even a f/2.8 is going to do it for you with your current body - you will need higher usable ISO to shoot indoor party shots without flash. The new bodies - even the T2i has ISO up to 6400. (I hear the 60D is also a very good camera.) I find ISO 3200 is very usable on my 7D. Think about how many stops you need to get the shots you want, and at what shutter speed is good enough. With good IS you can get away with hand-held shots much below 1/60th. You could get a T2i or 60D and a 17-55 f/2.8 for under $2k and the combo of the faster lens, the higher ISO capability, and the IS on the lens should be just fine for what you are doing. I also agree with the previous poster about going with the 5DII and 24-105 - if you want to wait to spend that much money, that is clearly a much nicer setup.
As far as getting a lens that will work on a Full Frame camera in the future - I say buy the lens for what you need now. Technology changes too fast. You can't predict what will be exactly right for you 1 year from now. All good Canon lenses hold their value. The 17-55 is a good lens and will hold its value. If you keep your crop camera and add a full frame to your collection, then you will want to keep the lens anyway. If you sell the camera, then you can seel the lens as well.
As far as the dust issue - it is real and from what I have read, the dust comes in from the front lens element. Some copies of the lens are sealed better than others at the front element. If you are OK with using a UV filter on the lens, you won't have an issue with dust. I put filters on all my lenses to protect them. Some people don't like them.
I ended up purchasing a 7D 2 months ago and held off on the lens decision wanting to see how the higher ISO worked for me (the decision at this point was between the 17-55 or the 24-105). I was taking candid shots of my Son's pre-prom dinner with the 18-55 kit lens I have, and realized that the focal lenght worked well, the extra stop was needed, and for all-around use the 17-55 was the best lens for me.