The USB port has been noted here often as something which should be suspected if seeing disconnection issues between the RC and the mobile device. As such, there is probably a demand for a known working part. As for price, well then I have no clue without doing some research. In any event, I'd say it's probably not something to throw away.
The only possible problems are that if the spare board is for a GL300A it is not compatible with GL300C or GL300B. GL300C and GL300B are compatible with each other. And is the board an actual functional board? If it were me, those questions need to be addressed before putting it up for sale. I’ll do some checking on it after work if you still need answers by then.