I have 18 sites in total, but need to replace the rotor bodies (10 of those). My parts came today and for my 8 spray heads I just did what you are suggesting. I could have replaced the spray bodies as well to get some pressure regulation at the heads (inlet pressure may not be ideal) but figured it wasn't worth it for 400 square feet.
In any case @Irwhit may have a different situation (better or worse), so I was just providing my numbers as an example. There are plenty of variables, but dollars aside there is value in uniform precipitation.