Well, the main reason woodcutter is weak is that it's a terminal. Re: using +buy to fuel trader, I can't say it's worth it. Consider that a hand with trader in it is going to be able to gain silver easily anyway by trashing estates etc, so acquiring +buy for the off chance you have it collide with a trader (and hoping you have something useful in the remaining 3 cards), isn't a very effective strategy.
Furthermore, buying curses and swapping for silvers *does not* deplete the curse pile. You gain silver instead of the curse. You don't gain the curse, trash it, and get a silver instead.