Subjective takes too much work.
I'd lean on someone else's work... perhaps PM Chase Stuart.
If I had to do something from scratch, I'd use VBD from here:
http://www.pro-football-reference.com/players/P/PalmCa00.htm#all_fantasy
I'm not sure what I'd do with it, though - VBD/year, maybe? I'd probably try to find some cutoff players at each position and see what their stats look like. Maybe percentage of seasons with any VBD is a better guide? Total years with any VBD?
For example, Ryan Tannehill is an NFL success in that he's been a starter for five years... but he's a fantasy failure for the most part - if you're starting Tannehill, things have gone wrong for you. Looking at his page, he has 13 VBD over five years. Sam Bradford has been a starter for 6-7 years, but has no VBD. Maybe somewhere around 3 VBD per year is a useful QB? Dalton has 29 over 6 years, Alex Smith has no VBD over 11 years, Jay Cutler has 63 over 11 years...
Let's look at WRs. Brian Hartline had 4 VBD over 7 years, Tavon Austin has 16 over 4 years, Kenny Britt has 20 over 8 years, Brandon LaFell has 13 over 7 years, Az-Zahim Hakim had no VBD over 9 years, Koren Robinson had 50 over 8 years, Roy Williams had 60 over 8 years, Marcus Robinson had 73 over 9 years (all in one year). Maybe 3/year again? Perhaps that works across all positions.
Poo, they don't have VBD listed for defensive players.