Hey there Doc,
My shallow keeper league is about to start, and I thought I had my keepers set, but now I'm not so sure. First the settings, which are a bit odd:
1pt/20 yards rushing/receiving/returning + 3-pt bonus @ 100 yards
1pt/50 yards passing + 3-pt bonus @ 300 yards
6 pts per touchdown (any kind)
Roster: 2QB, 2RB, 2WR, 1TE, 1K, 1DEF/ST, 4BN
2 Keepers - draft 2 rounds before previous year's pick. FA pickups count as last-round picks.
So, given these settings, QBs are much more valuable, and RBs aren't so much. I had planned on keeping Frank Gore (7th round last year), and Chris Johnson (FA pickup), and then going with a 2QB/2WR draft strategy for the first four rounds, but then I realized that I had Kevin Smith (FA pickup) on my final roster as well.
Last year, Gore was worth only 12 points more than Smith in this league. If I kept Smith in the 10th round instead of Gore in the 5th, I'd have a better chance of grabbing a top TE, or a 3rd QB/WR/RB that slipped through the cracks (this often happens in our league -- last year I got Boldin in the 6th round). Also, if I leave Gore out there, it's more likely that somebody will grab him in the first round instead of a top QB/WR. Finally, because of the weird scoring settings, it's possible to get top RB production out of a guy like Darren Sproles or Leon Washington who racks up tons of return yardage, though it's hard to count on that.
The major downside that I see with this is that Gore is capable of a huge bounceback season, so it's really a question of whether Gore's superior upside is worth the difference between a 5th round pick and a 10th round pick.