I've used the Pan/Crop tool to soom and reframe clips. I realize that after zooming the sharpness of the picture will decrease. Can Vegas doing anything to improve the sharness of a cropt and zoomed event? What about supersampling?
Supersampling is related to interpolating frames when you slow down a video clip... so I don;t think that will help in this case.
How much have you zoomed in? If a lot then it will be difficult to improve the situation. But... you might like to try out the sharpness FX. Have you tried that yet?
You also might try convolution kernal with mild settings and also the
unsharp mask filter. The problem is you are dealing with "after the fact"
resolution which usually means you have to create something out of nothing. Color curves might also help.