I put a 1/2 inch phenolic spacer on my car. It helped out a lot with heat soak.
Only other benfits I know of is if you use an open spacer you will pick up a few top end HP but may lose a few down low HP and if you use a 4 hole spacer you will pick up some down low HP but may lose some high end HP. But I don't think it is much at all. Nothing to wory about I don't think. Mostly just the heat soak thing.