As for the classic parts it can bring you some cash, but most buyers would want proof that the cards are actually working.
If you sell the BPPC and the BVision along with the 256 MB ram it should be able to fetch around £200 on eBay if it's a 040 model, plenty more if it is a 060 model.
But why not rebuild the A1200? If you are certain the BPPC and BVision are working, it can't cost much to replace a faulty motherboard? Or what is the problem with the computer?