As usual 4W is dead right, working on a single campaign is a lot of work in itself but would give the group a track record.
Also I would be careful about leaving out the historical stuff. If a site was for example surrounded by DMV's and so Roman stuff. by fighting to preserve these might help the case of the ancient monument in question. Often you are fighting a tide of local ignorance and by switching to a new item of heritage under threat you can bring people round a lot easier to the idea of it being an area of important heritage.