So I realize I really need some low light capability. At night and on the rides it was a challenge with the 15-85. Most of the time you could not use a flash and I was at 3200 ISO (I even went to 6400 a couple of times)
Looking back most of my indoor shots were a lot of different focal ranges (many at the wide end) and I doubt the Sigma 30mm would of been usable since you do not always have a choice to move around indoors.
Though it is the one lens that would have seriously improved your low light capability, at about 2 1/3 stops wider.
My question is, if I had the 17-50 Tamron f2.8 nonVC for indoor use how much would it of improved my ISO or pictures?
You seem to be confusing aperture with ISO sensitivity. One can affect what you need to do with the other, but they are independent variables.
In any case, f/2.8 is only 2/3 of a stop brighter than f/3.5, which is what you have at the wide end. It won't affect your wide photos much, though at 50mm, it will give you a bit more capability.
The Canon 17-55 f/2.8 IS USM would give you more flexibility, with its excellent IS implementation, though at twice the price.
Here are some examples:
1. Some of the really dark pictures from the rides I was at f3.5 at 3200 ISO and they were still not great. What the f2.8 of been able to capture the shot?
2. If I had indoor pictures at 3200 ISO from f4 to f5 then with the f2.8 what ISO would I get and would I be able to avoid using a flash?
1. As I said above, f/2.8 isn't really that much brighter than f/3.5. You could crank up the ISO to 6400 just as easily.
2. f/2.8 is one stop brighter than f/4, so you could go from 3200 to 1600.
Don't be afraid to raise the ISO. The image quality of modern dSLR's at high ISO's is quite remarkable. I've printed ISO 1600 photos from my old 40D at 24 x 36 inches and they look great. Just be sure to be shooting in RAW.
If you really want improved low light capabilities, your best choices are that Sigma or a 430EX. For the wedding, I'd suggest the flash. Don't forget to spend some time learning how to use it correctly, which means bouncing it most of the time.