Lamentably I'm in a similar situation :/

In my guild there's a dozen healers, which I'm one. Out of them, I'm generally one of the best performing; but am also one of the newest. So I get sat out of many fights, so the more senior members can gear up and get badges. Mostly I'm not a first choice unless more senior healers aren't on. I feel like the main reason they let me hang around, is because they know I'm good, and don't want to lose access "just in case". But definitely, I'm not getting that they really have my interests in mind.

While I understand why. They want to be loyal to people who have demonstrated their willingness to stick with the guild. In the end the practice is unfair to new members; and not even based on merit. I've not left because I actually like the membership. But don't think I haven't wondered if I'd be happier somewhere else. The main thing I'd recommend is make sure to PUG 10 man ICC, and VOA when it comes out. Keep your gear current. Maybe don't even show up for raid nights while the "senior" members have their fun. Then in a month or so when everyone gets bored, they'll be begging you to run if you can wait. If you can't, then take your time and look around for a guild that will appreciate your efforts better. It is a game, and if you're not having fun, then what's the point.