Yep, I'm in the Plot Bunny club also.
And for most of my life I would let the bastards win, and start writing the new idea. Well, needless to say I'm 25 and only have 1 short story finished, and am approaching the completion of my first novel.
I have several ideas, maybe 10 or so, that I want to get to, and they're itching at me all the time to get out of my head. But I think I've got a handle on it.
It's mostly just telling those ideas that I'm not ignoring them, I'm just giving them time to mature. That seems to work for a while, appeases them and keeps them quiet while I work on the current project.
Plus, I just keep the goal in mind of completing something. I'm anticipating what it's going to feel like when I finish this first novel. That's what's motivating me right now. But it took me a long time to finally throw off my gloves and say "All right, that's it novel, you and me, right now, it's on." I think when I did that, and the other stories saw the determination in my eyes, they kind of toned down and waited their turn.