Setting a price for Spica TC50s

The foam surround on the Spica woofer is known to rot (perhaps the cause of your buzzing), and I don't believe that exact woofer is still available. A replacement woofer would most likely require a change in the speakers x/o. Collectors of vintage speakers for that reason buy extra examples, just to have spare parts, as do restorers of vintage automobiles. I restore vintage drums, and buy damaged drums just for the parts.

If the surrounds are damaged, they can be replaced. At a cost of ~$30/driver.

These speakers, as is, are probably only worth $150, and only to one who already owns a pair and wants backup parts, or one who wishes to recondition. 

I had a pair of the TC-50 years ago. And one of them started to buzz. I contacted an audio-savvy friend who told me the quick fix, which indeed fixed it. 

The mid-bass driver is doped by something as high tech as glue. The glue can sometimes start peeling off and the splinters that are lying free and projecting above the driver vibrate and buzz like crazy. 

The fix-apply a small amount of Elmers Wood glue with your fingertip to the driver and rub it around to distribute it evenly. I am guessing something like 0.5cc is sufficent. You will see the fiber of the driver (is it paper?) suck this thing in, and it will now take on a shiny look. Allow it to dry a couple hours and play. Buzz should be gone. If it has improved but not been eliminated, re-apply one additional 'coat'. 

If this works you may also want to treat the other side. 

TC-50 are great speakers. I took them as far as I could with the Sound Anchor stands (pretty much a must, even for the $300 ish price they commanded in the 1980s), and redid the crossovers with higher grade capacitors.