It's well documented that this is amongst the best Nikon lenses ever made, but this is not reason enough to hold on to it. I very rarely use the lens. I can very easily get 2 or 3 lenses I just think that the several other 28mm's are good enough. I don't need a lens to be PERFECT. Contrast is more important to me than sharpness, and most Nikons, realistically, do perfectly fine on both fronts. It's going to take a pretty good eye see the difference between the 2.8 and the 3.5, from what I've read.
Wait you're getting rid of the 2.8 for the 3.5? I thought you were going in the other direction (2.0). While the f/3.5 lens may be adequate I'd stick with the lens you know. I can't see why a 28/3.5 would be more useful to you. Then again if you're just looking for other focal lengths, then alright.