Amen. Whereever you may be, there is always a trail org, a park group or open space org, etc that could use a helping hand.
I call it cross-trail karma. Besides being rewarding work (you give back, and often get to go to areas most people aren't allowed), it is fun.
A little sweat equity helps everyone.
..and here is my standard boiler plate post on post-trail (and PRE-trail!) adjustment:
http://www.pmags.com/joomla/index.ph...ost-trail.html
A lot of it is what Spirit Walker said: Find what you loved about the thru-hike and bring it into your life....
Good luck!