Okay, so I ended up with a pretty good system for the slopes, but I'm going to have to make one bin for "miscellaneous slopes" because I don't have very many of the same type.
If you get someone to help you sort, make sure it's someone who goes along with your system, and doesn't start making piles of other stuff that go together, even though you have nowhere to put it, claiming that they can't look for one kind of piece with all the other crap in the way. In other words, don't get my mother to help you. Inb4 Warhead.
Seriously, I told her to look for plain 1x2 bricks, and she ended up having like ten piles of other pieces she thought would be good to make piles of. While this may be efficient, I had a system where I'd pick out one kind of piece at a time and put it in a bin, which would gradually make everything easier to find. Who knew someone would find it so difficult to follow simple instructions without trying to "critical think" their way into making it more suited to them.
Anyway, it looks like I'm going to have to pick up some more storage units from Walmart or something. Not enough drawers!