Why would you want to coat an intake manifold? I haven't heard of people doing that. I can see why exhaust manifolds are coated. Coating an exhaust manifold will keep the exhaust stream hotter, maintaining more exhaust gas volume and velocity for quicker spool and exhaust evacuation. Also it keeps the engine bay cooler.
But I'd think the intake manifold should want to sluff off as much heat to keep the intake charge as cool as possible for greater air density. I think intake manifolds are aluminum to remove heat from the plenum faster. Coating it would defeat that purpose.
But if there is a benefit to coating the intake manifold, I'm up for some edumacation.