it's really going to muffle that much more noise? i already think the car is might quiet over my 2 trucks. so no complaints there.
heat dissipation was a concern of mine. figured the engine would be cooler if i didn't have the cover.
as for staying clean, the cover is just as likely to get dirty as the rest of the engine. so sooner or later you're cleaning the engine and the cover.
i've got other battles to fight.. not really worried about the cover.