What we can observe here is that while the elite RP core does positively impact pitching statistics, the inferior RP core simultaneously NEGLIGIBLY impacts the pitching line -- while the superior RP core lowers ERA well below the projected "what it takes to win" threshold (while also lowering WHIP a sizeable chunk), the inferior RP core only increases ERA by .06 and whip by .01. With smart drafting of SPs (who have much more impact on cumulative pitching statistics than RPs, mind you), this tiny impact of the inferior RP core could easily be offset, while gaining the benefit of a 3/4 category hitter or two early in the draft (by forgoing the elite RP in favor of an "inferior one").
What is very roughly observable here is the overrated impact of RPs based on draft position. Inferior RPs can easily put up comparable counting stats without hurting your ratios if you draft smart. Comparatively, late game hitters (minus sleepers, which can be harder to effectively forecast) generally cannot produce comparable offensive numbers to early round hitters. Come picks 180+, the hitters left in the pool are generally one category guys and offensive gambles. If you go with an early RP, late hitter strategy, you are maximizing risk (by forgoing more reliable/valuable hitters) and minimizing overall return, which is somewhat irrational in the investment game known as drafting. Smarter investment would call for the strategy of simply ignoring RPs until the later rounds (or just ignoring saves all together and focusing on the other 9 categories; why not try maximizing 90% of your potential against balancing 100%? It is equally as viable if done properly).
A lot of this knowledge is "conventional wisdom" for baseball drafters; I'm just putting some rough numbers behind the assertion. Now that that is established, let's move on to the point of my post: rules of thumb for drafting Closers (btw, I should go back in my post to modify all references to RPs as CLs, but you can infer what I mean and as I mentioned earlier, I'm lazy).
If it isn't obvious by now, I think closers are overrated. I rarely draft them (because so many guys lose their jobs midseason), but when I do, I like to look for bargains. I look for guys who meet the following criteria (in this order):
1) Job security
2) Save opportunity potential
First and foremost, if you are going to draft a closer, you want to draft a guy who is going to close. Why waste a pick on a guess (ie, who is closing in Seattle for 2009) when you can probably pick up the person who the closer out of spring training loses the job to off of waivers within a week or two? Why also waste a pick on a closer who has a better RP who may unseat him from the closing role behind him? To me, it seems like a waste of a pick that you could spend gambling on a guy like Denard Span or Shin-Soo Choo.
Secondly, I like a guy who is going to get the chance to save games. This doesn't mean a closer for an offensive friendly team like the Red Sox or Yankees, but closers for teams like The Pirates and Royals, where every one of their 70 wins per season is a save opportunity. Last year, I got Matt Capps, Joakim Soria and Brian Wilson at incredibly discounted prices and they paid off big time.
If you want my recommendation of who to draft, I'd recommend Brandon Lyon (because no one in Detroit is really healthier than him who can throw strikes), Brian Wilson (who has great stuff and no one to unseat him), Heath Bell (the Padres are notoriously committed to keeping their closer the closer during the season, no matter how hard he struggles) and Grant Balfour (the healthier, younger, better option for Tampa; Balfour for Closer is as inevitable as was Obama for President).
That's all for now; it's late and I'm tired. Apologies for spelling/grammar errors; I just wrote this from beginning to end in one sitting and am (yes, you guessed it) too lazy to re-read/edit tonight.