For a quick easy detail trick, instead of tire foam, I use Silicone Spray... I learned this trick when I had a jet ski and needed to protect the engine from the effects of salt water. You can spray it all over everything under the hood (I try to stay away from belts though) and it leaves a nice glossy shine without ooking "cheap", and it wont damage rubber parts. I get it at Wal Mart, I think its Prestone brand for like $1.79 a can.
I dont usually spray under the hood, I just always pop the hood and wipe down everything that gets dirty with a damp towel. I find that if you start out using the silicone spray, and keep it wiped down weekly, it never really gets very dirty. The silicone helps keep any dirt from sticking, so it wipes off easily. It will also remove any remaining water, and prevents water spots. Of course, if you already let it get real bad, or if you drove through some mud puddles and theres crap all over the engine compartment, then use Protege5Gurly's detailing tutorial... looks like she knows what shes doing by the looks of her engine...