I got into Opeth back when they were touring the states with Nevermore in '02. They've been my favourite band ever since, even though I lost interest in following them so closely sometime after GR was released. As usual though, the new album has re-sparked my interest, and I'm always astonished as to how the band can reinvent themselves enough on each release to draw me back in. I don't think I'll ever be quite the rabid fanboy I once was (my job kind of prevents it) but that doesn't mean the band have stopped releasing quality music.
I do see the cycle you're speaking of though. A lot of the old guard on here left ages ago. Many got fed up with the newer fans, and used Opeth as a gateway to other, less accessible music. I went through a phase of distancing myself from Opeth, but certainly didn't believe I was 'beyond' them in any way, as some of the more pretentious assholes seem to think once they get bored of Opeth.... and let's face it, when you can recall every nuance of every song in their whole discrography, why wouldn't you eventually get bored? It's amazing that Opeth can enthrall people for so long, and then come back to do it again with each new album.