Are adapters that allowing lens change on cheap camcorders worth it?
Such devices do exist a reasonable amount of the time, but they rarely produce much in the way of quality.  There are exceptions, but they are fairly rare.  They do have their uses, but be aware that the results are most often marginal.  Your best bet to find them is generally looking around the various smaller NY/NJ photo/video shops that carry a variety of knock off products from around the world.

Make sure you are aware of what you are getting yourself in to with them.