It won't make any difference as long as you still have your source files. Think of a rendering as a take. If you don't like it, edit some more, then render again. The quality only goes down if you take the rendered file and use IT as the source as opposed to using the source files to render a 2nd 3rd or 50th time. The quality will remain the same. Even if you use the renderd file made using one of the DV templates you should be able to get at least 5-6 generations before you seen any quality loss.

Remember... Vegas doesn't change the source files in any way. Only the rendered file changes based on what you did in Vegas.