I just can't see not taking a RB (or 2) by the end of the second round this year. Of course everything depends on how the draft is going, but I don't see how you win without a top 15 preseason ranked RB, which is where you'll be if you skip RB in the first 2 rounds.
I'm sure one of Murray, MJD, Miller etc is going to break the top 12, possibly top 8ish. It happens every year. But which one? That's the big downside. And 15 backs still leaves 7 other owners without a RB2 on their roster past the second round in a 12 team league so you're competing with them plus anyone wanting to flex a RB. You just have to hit on RB later, against a shallow pool of unknowns (Miller, Bell, Lacy) injuries (MJD, McFadden, Murray) and RBBC (Carolina, CIN). It's ok to try with one guy to pick up Rodgers, Graham, or Mega (maybe Brees) but I think you will regret not taking someone in round 2 if you do.
The whole premise of "I'll just get someone like Bush or Miller later" is kind of a weird stance to me. It means you know you're getting them or are going to reach for them. It's easy to theorize a lineup taking WR/TE early for instance, another thing entirely to actually get it.
Enough people pick non-standard (ie not RB/RB) now days in most leagues I've joined in the past 3 years that upside down drafting just doesn't work. The premise is that you are zigging while everyone else zags. You're getting elite production from WR and QB and fliers on RB that noone else is taking because they already have 2 and now need other positions. It's just not working out that way anymore. Fantasy Football used to have no QB taken in the first 3 rounds. Maybe 1 or 2 WR in the first 2 rounds. It's just not that way anymore. You're not the sole person vying for the Lamar Millers and Eddy Lacys of the draft anymore, so relying on getting them is a fools game
The times I've gone WR/WR, I've typically grabbed 4-5 RB's in the next 8 rounds. The additional outs, so to speak, enhance your odds of finding solid value. You aren't gambling that any one of the guys pans out - you're gambling that at least two pan out. I don't think all of the 'safe' RB1s offer the security that a top 4 WR does, and I certainly don't think the RB2s do.
So the question to me boils down to, do I feel safer grabbing 2 RBs in late position and throwing a bunch of WR's at the wall, or vice versa.
Have you gone WR/WR this year though? If so care to share a typical roster you have? I went WR/TE in a league last year, but I was pretty sure I could get a couple of guys later in the 3/4 rounds (got Gore and Martin) And the guys at the end of the first were not interesting to me (Matthews, McFadden). But then again it was following one of the craziest years in FF for QB do they flew off the board really fast in standard scoring leagues.This year I see limited options in the late 3rd early 4th for decent RB gambles. Bell is as close as it gets and he doesn't exactly inspire confidence.
My typical WR/WR strategy from mid/late position right now (some tweaks depending on if 7th or 12th,of course:1: Calvin (strategy hinges on starting with him)
2: 1 of Dez, Green, Julio
3/4: 2 of DWilson, LMiller, LBell
5: Bernard or Vereen (used to be able to get both at 5/6, no longer)
6: I like taking RG3 here unless QB's really slipping. I've also taken V Davis, but his value may have skyrocketed past this now
7/8: QB and either Mendenhall or Hopkins
9/10: target list includes Michael Floyd, Pierre Thomas, Danny Woodhead. You have to grab a Pierce, Andre, or Bryce here if you want one.
11th:Hillman used to be available here, no longer. Jacquizz Rodgers still is, but meh. Not a huge fan.
Late target has been Bilal Powell. Late late late target has been Chris Polk.
This is just a predraft plan. You have to be flexible if value drops, however.