I suppose I forgot to mention the bonus of the IS. I feel like having IS will prompt me to take my camera to more places (spur of the moment outings) than in the past.
I tend to always use a tripod when doing most of my shoots (Landscape is my most shot subject). I tend to miss a lot of shots because I don't want to or dont have time to take out my tripod and set up for the shot. However, IS would allow me to narrow the aperture a bit more and take lower ISO shots that I couldn't have done hand held otherwise (This is in a situation where I don't have my tripod with me, mind you).
So, I guess what I'm saying is, The IS should allow me to take more shots in situations that I am ususally less comfortable, and it will weigh less, and will be more insconspicuous than the 24-70.