Dogs and Their Weird Sense of Smell

Whenever I come home and kick off my shoes, one of my dogs immediately likes to run up and stick his nose deep into them and rub his face around for awhile.  You know, really get the foot funk deep into his nostrils and spread all around his face.  Now dogs have way better senses of smell than us and yet they seem to like the smell of gross things.  They enjoy sniffing each other's butts, smelling the garbage and then subsequently eating out of it, or smelling any sort of poop or dead animal they encounter on walks and possibly subsequently trying to eat that as well.
  I get that smells contain information for them, but I would think as rank as that sort of stuff smells to us, the last thing I would want would be to smell it even better.  I'm guessing when you're able to smell that intensely there are no bad smells.  Everything smells amazing and wonderful.  I wish I could smell my stinky shoes through my dog's nose.  He looks like he's quite enjoying himself.  I would love to be able to obtain the level of pleasure my dog achieves by rubbing his face inside my shoes.