24mm on a 1.6x crop body probably isn't too bad. I have done WDW and DL with a 28-75m on a 1.5x crop and was OK much of the time but missed the extra width for things like pictures at character meals, with nearby people, etc. I use a 16-50mm now and that works very nicely; it's pretty wide and covers a good, useable range. As long as you're not too worried about wide shots, 24mm will probably be OK; certainly a good bit better than 28mm. (Each mm is more noticeable on the wide end.)
In your case, I'd probably lean towards one of the wider lenses, like Tamron's 17-50mm. That gets you much wider and with an extra stop of speed vs the Canon for less than half the price, and you get IS on the current version, too.