When do you have too many bristleworms? Whenever I feed, this is the scene. I don't notice that they are harming anything in the tank. It's only a 24g cube, but some of these are 6-10".
I know others will have a different opinion but to me 1 bristle worm is already too many. I dip furiously to keep them out and so far have succeeded. IMHO I don't want anything in my tank that can sneak up on me and put a hurting on. But if you're comfortable with them that's all well and good but yeah a 10 inch worm in a 24g is a bit too big