I've only owned one for a little over a year and its one of the first generations of Gerber ION Solara's they rushed to the market, so my experience is limited.
I'd have to say that for the revenue it generates, the competitive advantage it gives us over nearly everyone without one in our area, and the amount of productivity its capable of when running optimally, its not unreliable at all. A couple times per year, it acts up with minor issues and we need a service call done which takes a few days to arrange, but once here we usually get back up and running within a day.
For a 6 year old machine, that easily produces over $125,000 or more in revenue every year, that's not bad.
I'll say this, my predecessor and his employees did not take as good care of it as we do, and our long time service tech who installed the machine and still services it has told us that these type printers like two things. They run way better with frequent and heavy use and they run better with proper care and regular cleaning.
So, if yours keeps acting up, double on up on your internal maintenance and cleaning and try to push it harder by expanding your market. Do you do any wholesale work for other sign shops, graphic designers, ad agencies, etc.? Those are great places to start.