Funny that some cite Space:1999's bell-bottoms as aging the series, but in reality, the bell-bottom look made a temporary comeback in the real 1990's--the early 90s as the 70's was in vogue again. This was seen in the new appreciation/marketing of Blaxploitation movies, Dazed and Confused, Tarantino's early films feeding off of 70's references, a golden age for 70s music reissues and compilations released, and later that decade, That 70s Show's debut on TV. So with that said, one could argue that Space 1999's bellbottoms were just predicting the retro 70's movement that would happen of the 90's.
That's an interesting point, although in that case bell-bottoms were probably one of the few
things that Space: 1999
got right about the 90's.