Does blocking off the EGR do anything? My logic is that it will keep hot dirty air from entering the intake plenum, therefore allowing the air to be slightly cooler and cleaner?

 

EGR ciculates already combusted "air" essentially making it inert in the combustion procress if it goes though again. Putting an EGR block plate prevents the exhaust gas to recirculate allowing you that much fresh combustible air into the cylinder and reducing the intake air temperature. It only benifits power in the end to block it off.

 

This has been discussed many times before and i think the overall outcome of it was that its such a small amount that you wont notice a differance.