I have a rule that I like to call the Michael Finley rule (although it could just as well be called the Karl Malone Rule): "worry less about a drop in numbers in a senior year than a jump in numbers."
That is, if your guy was crappy until a sudden surge in his senior year, don't draft him: he's a flash in the pan. But if he was good but his numbers dipped in his senior year (like Finley's and Malone's) then this is probably because of having to carry more of the load and just be glad because it'll mean he'll drop in the draft to where you're drafting.