I saw some pics on another forum of the steam boiler element of a Vivaldi after 6 months of use, somewhat heavier use than mine. Based on that and the softness of my treated water, I'm pretty sure I can go a year. And if it's only an annual thing, it won't kill me to take the boiler completely out and clean it and the element properly. I'll have the boiler out and empty soon to insulate it, and will see how it looks after 8 or so months.
Then, as long as I'm having that much fun, I'll open the group boiler up too. But that boiler is smaller and the water is exchanged so much more frequently that I doubt there'll be any real need to do anything with it.
Noob qualifier; any and all the above is open for pot-shots.