I'm always TEMPTED to upgrade but so far ever since I got my Janome 6600 I've been really happy with it and don't intend to replace it. I did upgrade my free-arm/portable machine recently; I gave away the one I had and replaced it with something much nicer. And I'm seriously considering buying a sit-down longarm machine in the next year or so but I don't consider that an upgrade, more of an addition to the "fleet".
I think I am at a point where point the machines I have are really good and do everything I need, and unless my needs change or something breaks I don't think I will upgrade or replace my current machines for years to come.