If you're waiting on drafting closers, keep an eye on the teams that have a competition currently (Colorado for an example). Street is going several rounds before Corpas, and neither one have it locked down yet. I'm more than willing to spend a last round pick on Corpas, even if he's the odd man out when the season starts..
Also, Kevin Gregg is going really late or undrafted. Though Marmol will have value even if he's not closing, drafting Gregg in the last round or two is a bargain.
...Boston papers now and then suffer a sharp flurry of arithmetic on this score; indeed, for Williams to have distributed all his hits so they did nobody else any good would constitute a feat of placement unparalleled in the annals of selfishness. -Updike