I've never seen the point of drilling barrels. Possibly because I'm exclusively a xenos player and dark eldar guns aren't drillable (I am certain you'd destroy the model if you tried on most of these weapons) but even on rank and file marines it seems more bother than it is worth. A simple dot of black paint in the middle of the barrel is far faster, less finicky, not capable of destroying your model and looks identical on a tabletop quality model held at arms length. If you want to do it for your champions that makes sense, but trying to argue your opponent shouldn't use their troops without drilled barrels is snobbishness at best, if not outright cheating and bad sportsmanship. *eyes Cpt Codpiece*
I feel that obvious mold lines should go but if you have traces left in out of the way places that will only be seen on close examination then that's okay. I do agree that display models done by professionals for exhibition should be held to a higher quality though, and that definitely includes the 'Eavy Metal team.