If you plan to have the car 'judged' in original class judging, putting the top on would add 'points'.... otherwise, I'd leave it alone as is unless you WANT the top on it. If 'original judging' is how you have fun, then the top should probably be put back on, but the real answer to your question is 'what is FUN to you'?
PS> I traded for an orange/black Z28/RS back in '75 or 76, and my original plan was to *restore* it without the vinyl top ( because back then, my logic was: vinyl tops add weight, hold water, allow metal to rust from underneath, etc'! Now, after the car sitting in my garage for 30 yrs (undriven), I've decided to keep it as 'original as possible', even plan to finish cleaning and show it (hopefully) in the original unrestored class at the nationals.
Gary / 69Z28-RS