How much would I gain by getting the 24-70mm

Hey guys and gals.

I have the kit lens (28-135mm) that came with the 50D, and it doesn't seem to have enough width to cover when I'm indoors. So now I'm looking at the Canon 24-70mm f/2.8L based on the great reviews I have read.

I'm pretty much a newbie when it comes to DSLR, so looking at the number 28 versus 24 (not really concern about the length right now), doesn't look much. Again, I'm might be completely wrong at this, so my question is:

How much more width would I gain from 28 to 24? Or am I actually looking at the wrong lens for the type of shooting I'm referring to?

If so, what do you guys think is best?

Thank you in advance, much appreciated.