Value is considerably diminished for 2 reasons; these can only be owned by those who are grandfathered for 12(3) and the fact that the government will not issue ATTs for owners to take them to the range.
USGI M14 parts are in demand for use on the Norinco rifles, so the value is basically in the parts, except for the receiver which is a paper weight.
Its all too bad. As far as can be determined 12(3) converted autos have never been used for criminal purposes, but nevertheless our country is a much safer place now that they are off the streets.