I was unaware that Washburn made harps. The quality of their guitars varies depending on when they were made and in what country and what quality control was like at the time. I’ve seen some decent ones and I’ve seen some shockers. So if they are made by the same company, I would do some homework on it first (which it looks like you are doing).
As for collectibility, I’m of the mind that ALL musical instruments are collectible. Probably why I have three banjos and no girlfriends. I’n general terms, a “vintage” Washburn guitar could be seen as collectible I suppose.
Good luck on your quest