hey mate, i recently got a z tune vent moulded into my 32gtr bonnet i noticed around 15+ degree drop in engine temp.
and rain gets in. but i dont really notice it bieng dirty or anything. just made sure the seal around my cam covers and coils is in good form!
just adding to the thread after reading the rest of it.. i have been pulled over by police on a number of occasions and nothing ever mentioned about the bonnet, or headlight.. or anything for that matter.