I purchased a Service Maintenance Agreement with my Bernina 440, and when that expired I purchased another one. It covers anything that goes wrong, service and parts, and is well worth the money. Because it doesn't cost me anything additional, I take the machine in whenever we're going out of town for a week or more, usually about twice a year. The machine gets checked out, completely cleaned (I am diligent about regular cleaning but I can't get to everything), and any electronic updates are loaded into it. The dealer where I purchased it has an excellent reputation, and they give me a good estimate of how long the repair shop will have the machine.
I do have several backup machines, and they don't get the same treatment. However, they're from another era and don't expect to be pampered.