sad to hear, but i've got to say that i think that you've made the right decision!
You've got a really good thing going with the other 2 products and moving forwards (at least for a while) with evolution, rather than revolution makes the utmost sense!
Hopefully passing this on will mean that the profits from the other two start to increase rather than being sunk into the 550 and you can get back to a position where you're don't have quite so many worries, and then if/when the time comes to introduce a 3rd model you can do so and enjoy it more!