I have the same problem. However, based on my area - these recruiters all stem from about the same half dozen firms or so. I usually will keep one good contact with each firm, and if someone else from the firm messages me I will forward them to the good contact that I have at the firm (this shows my, albeit lazy, loyalty towards this particular recruiter).
There are a couple of reasons for me doing this. They will build a profile for you, and watch you more closely if you keep in contact with them. This will allow them to see/know your current employment, the length of that employment, and any future promotions you may gain while in contact with them.
I let them know that I am currently not looking for a new company to go to. At this point, they will usually ask a question to the point of "What will it take for you to leave?" - I set the expectations really high. Much higher salary then what I'm currently getting, and more senior position. That way, if they do ever contact me with a position meeting this description I know it's going to be an offer I can't refuse.
Another, more selfish reason, for staying in contact with a few recruiters is most will take you out to lunch or dinner for free every month or so - and I don't know anyone that doesn't like free food.