the heatsheild actually does serve a pretty simple purpose... to sheild heat from the rest of your engine. I've heard from some guys who took theirs off that wires and hoses closest to that area began to melt and I'm sure the under hood temperature would greatly increase. I'd leave the exhaust manifold alone and just maybe touch up the heat sheild with a new coat of black or silver paint... If there wasn't a specific purpose for it being there then i doubt honda would put it on just to cover their ass.