This.

If I recall, there is a particular Perth WRX owner that made a ridiculous amount of power on a VF series turbo and an EJ207 a few years ago..

When I had an in depth conversation with him about the build, he outlined all the small mods he'd done.. and apart from the usual power making modifications and a shitload of boost, the little mods actually do add up to something big.

If anything, they increase efficiency and the secret is to keep the heat in where it should be, and keep it out of where it shouldn't be.

It's a diminishing return when building a car, after making the big mods, the small things cost a lot for minimal gains.... so when you can get something that might gain you 1HP (or at least keep your car making its maximum HP even when things start heating up), for $25, then that's good going.. people spend $500 on things for a few HP without even battering an eyelid (silicone intakes for example), so IMHO, this mod (and phenolic spacers) is an absolute no brainer.