Moss is the type of guy I've mentioned...a rookie deal guy.
If we got him in the 4th round, we could have him as a backup to Drake this year, then let Drake walk. Moss and Edmonds next year then let Edmonds walk, then Moss for 2 years, etc.
Its got to be a rotation. Now, every once in a while you stumble across a great RB who is worth that 2nd contract, or a Frank Gore type who seems to hold on and be productive for 20 years...but the vast majority of these RB's can and only be counted on for their rookie deals. Build a great O-Line and offense in general, let these guys make a name for themselves here, then go get paid somewhere else and start the cycle over again.