This resin = C, skunk = B idea.
I think the reason most people, certainly me and all of my friends switched to skunk or grass (cant really be sure what we are buying, it gets us ****ed regardless) instead of resin, is because resin is stupidly easy to cut; from just looking at it, you can tell it's unpure mixed with all kinds of horrible cack, and it is quite horrible to smoke. Grass on the other hand is a little bit harder to cut down with horrible stuff, obviously there are the usual tricks like sand, powdered glass and silicon packing materials but cutting with that crap doesn't seem as common as cutting resin with soap, diesel, plastic, dirt, poo and other nasties.
I think all that would happen with an increased classification would just lead to a load more unpure herb type cannabis, which doesn't really help anyone.
Just for the record, a friend of mine definately had some that was mixed with a smattering of smack and a crapload of sand to make it addictive.