I think a lot of people can let it get to their head, play hero and act like if they catch some minor crime, it makes them special. On this point, I'd say it'd be a nuisance. I think all the best to a community if it can prevent thieves and murders and rapes, but I'd think that even without the label of "community police", people should try to help with this.
I think that the energy could be much better employed making a community shelter, or a community learning center, or a community garden, or a community kitchen -- something that brings people together around productive peaceful things, rather than putting them on the lookout for each other like we would be in Communist East Germany. I mean, seriously. Normal people don't have the training to solve real crimes, just to make trouble for some harmless criminals smoking weed or gambling in a corner. Better have them helping each other out instead of condemning each other out.