He's on the 53 now. As long as you can figure out the $$, I dont see a roster or market competition issue with keeping both Woodhead and Vereen (isn't V still under rookie contract through next year too) through at least part of camp. the roster limit is 99 (or something ludicrous like that) for the start of camp. You can alway consider TRYING to trading one rb for future draft picks at the point where you think you have too many. There are too many injuries and guys who fall out for other reasons not to keep them around.
this isn't as simple as Woodhead or Vareen. Sciz made a good point when he noted that we are definitely going to have 4 TE's on the 53 next season....at a minimum. I see Boldin, Ridley and Vareen as locks as base RBs I also see a big SY RB/FB as a need next season, like a Larsen or the Navy kid as a possibility. Finally there's the investment we made in Demps, who will have a full off season + to get into football shape as KR/PR/3rd down RB who has all the same skills as Woodhead but is quicker, faster, younger, and cheaper.
The question isn't so much is Woodhead better or worse than these players but are his skills redundant and/or replaceable. Does his experience and reliability outweigh the risk of developing another player who can take those snaps with similar or better productivity
Are the Pats willing to give him guaranteed money up front, or is he willing to stay for a decent contract, but have to make the team in order to see the money. The last contract he signed was for 2 years and $1M (IIRC). He probably wants to at least double that. Its not big money but are you willing to pay Woody even $1MM/yr for 3 seasons, when you have Vareen and Demps in the wings
Finally, given his likely reasonable price and the reputation that Pats RB's have as guys who don't fumble, run hard, and are reliable blockers, there are likely teams who would play Woodie that much who don't have a Demps and Vareen in the wings.