I'm on my 3rd 400 for similar reasons. I have to bite the bullet and realize that it's what I consider a "core" bike. I'm PO'd at mine right now, as a matter of fact, but there's no way I'll sell it. After I sell one, I always end up missing it too much.
Put your 550 in moth ballsif necessary, and get a newer used bike too. No need to pay full retail for new technology and supposedly better handling.