Yeah, definitely depends on how much you like the subject which will dictate how committed you are to repeating study. I was considering repeating Methods but chose to do Further instead mainly because I wanted to learn [hopefully I'll learn a bit :S] different maths. If I had repeated Methods I would probably get bored when it gets up to doing loads of trial exams :buck2: that would suck.
I don't think it will be beneficial for the normal student. Only a dedicated student will benefit, and seeing as a dedicated student should do well the first time, no I don't think it's a good idea. Unless of course you screw something up badly, but even then wouldn't it be best to learn something new? That's my view anyway. Not everything in VCE should be dictated by whether it will benefit your ENTER score and SS's.