Thank the Blessed Stars!
Someone already mentioned the Witch Mountain movies, and sort of the books. I know a lot of people have fond memories of the movies from their childhoods, but I love the books even more. I still re-read mine on a regular basis and buy used copies to give to new people to enjoy. This book was one of the biggest influences on my entire life. I know of exactly 2.5 people who have written fan fic about it, and I am one of them. The books are out of print and the current copyright holder is unknown. Alexander Key's son, Zan, died a few years back, and his heirs are elusive. Tony and Tia helped set the theme for many things I loved over the years.
I like a lot of obscure things that geeky, bookish people like so there are groups of fans but sometimes not very many of them.
This one is somewhat nostalgic but I go out of my way to try to tell or show people this one: The Legend of Bilie Jean starring Helen Slater and Christian Slater. This one fits right in there with the Buffy movie as a strange but more thoughtful than it seems on the suface teen film. I haven't been able to see it in ages since I moved away from the one library where I could find a copy of it still (on VHS not DVD). I still cry when I hear Invincible. Other than the close friends I'd shared this movie with myself or watched it with when younger, I don't know of anyone who even remembers this film. It really is better than the 80's hair and simple plot would make it seem.
And then there was/is Star Blazers/Space Battleship Yamato. I've been pining for this one for years. I tried to get the money to buy it, but it's horribly expensive. Maybe in anime fandom it isn't that obscure, but outside of those circles I don't know of people who like it or know it. I fell in love with my first 'honorable enemy' in Leader Desslok/Dessler. His swoopy cape was what I thought of when I first saw Darth Vader. I finally got to watch the first two seasons again recently, and it was as good as I remember. In fact, in the Japanese version, it was even better. Honor. Sacrifice. Duty. Love. I cried for joy watching them again.