Andy, If it where my car I'd take the whole car to bare metal for several reasons.
#1) I agree with previous posts that it's the elements that caused the clear to come off and the lower parts still "look" good but what happens if the degeneration of the clear has already started and a year or 2 from now that clear underneath your fresh paint lets go...Your the guy who painted it and will take the blame.
#2) It's going to take a day at the most and even on a bad say $30.00 worth of material...cheap insurance.
#3) Take the car down to metal, if you DA the car down to primer only chances of getting wave is much more likely and I saw the reflection in your Nova, it was straight and that's what you want. The car, from what your saying is straight right now, SPI and a little blocking will keep it that way. The red on your car is a fairly dark color...and you know what dark colors and any imperfection in the body are going to look like in the end.
#4) The only paint jobs that people ever talk about are the really good ones and the really bad ones. The nice thing about that situation is you get to decide what people say and think of your work and it's always easier to get more work when they say good things about it.
Take the little extra time and do it properly so you know what you have when your done. Even Ford under their paint warranty programs in the 90's paid to strip the entire vehicle, they didn't do it because they liked to give money away, they did it because they didn't want the problem to come back and bite them a year or two down the road.
Hope this helps