The Patriots are starting to employ that 'two back approach' which is so common in today's NFL...a running back corps by committee is the best way forward. Pat Kirwan wrote about it in his book...the issue in the past with running backs is that teams would give their best back the huge bulk of the carries (kind of like what Adrian Peterson is asked to do for the Vikes) and with that, their careers were drastically shortened.
Ridley is the speedier and more agile guy...I personally think Green-Ellis is the better power runner although I'm not knocking Ridley's ability to do it. You use your agile and speed guy in the situations which best dictate to use him, then you have your short yardage/goal line back (that's Green-Ellis). The committee approach is the best way forward and we'll continue to see it...but Ridley should definitely start to see the bulk of the carries in my opinion. There's little doubt about that in my eyes.
Having that approach prolongs the life expectancy of your feature back and keeps him fresh. The Giants do the same thing with Bradshaw and Jacobs. Vereen is the future at 3rd down back and I don't see why Woodhead hasn't got a future here. Re-signing Green-Ellis is a must in my eyes.