http://www.nerc.us/
NERC is probably the best bet in the North East. They're working on running two major events a year, one is at Motorama in Harrisburg, PA
Motorama Robot Conflict 2008
February 15-17, 2008
Farm Show Complex, Small Arena
Harrisburg, PA
The other large event is hopefully going to turn into a yearly thing at The Franklin Institute in October
http://www2.fi.edu/
Best place to find events is at
http://www.buildersdb.com
Another option would be BotsIQ
http://www.battlebotsiq.com/
As far as my thoughts on whether or not FRC teams getting involved in robot combat is a good thing, I think it's a great experience. I know for a fact that it has influenced 675's FRC builds for the better, and it's a great way to get new members involved early in the school year, since there are competitions year round and no set build periods.