I would agree that similar taste in music is not a necessary condition for a successful relationship, but it is a HUGE plus if it's there. An ideal romantic partner to me has to also be my best friend (or one of them, at least), and that is greatly facilitated by a common interest in not only attending shows, and discovering and listening to music together, but it also really helps integrate us as a couple into our social group of fellow metal-heads.
The last thing I want is to bring a partner along to gatherings of friends where there is a disconnect in common interests between her and my friends (or vice versa). Sometimes that's unavoidable, such as when my fellow Classics grad student get together, but my truest friends have been my metal bruvs, and LG is one of them.
This is not to say I dislike a partner having divergent interests and friends who aren't really my friends, but everything does need to be in the right proportions.