I would have to agree that JC's return in 1984 had so much potential, and it was totally wasted. I would add Nancy Frangione's return in October 1995. Cecile's previous returns were always a big deal for longtime AW fans. JFP brings her back, saddles her with the historically inaccurate storyline that Cass is Maggie's real father, then Cecile unceremoniously leaves town in the Summer of 96 never to be seems again. There was a time that AW would have done anything to have Frangione back on the show for the long term, but JFP was not really interested in using Frangione to her potential. Remember how they never gave her a contract and her name was listed in the credits with the under-5s who appeared that day and how they did not put her in the new opening credits because she was a "recurring" character. Had Frangione stayed with the show, she could have married Cass in the last episode rather than Lila.
That IS pretty great.
So many series I have yet to catch up with, I'll try to resist getting sucked back into old TNG episodes... for now. But such great memories.
And when did Spin get older than me ...