I take my computerized Bernina in about once a year. It costs me $85 and runs and sounds like a dream when all the lint is cleaned out. I've only had it in twice so far and the first time was a week cause the repair man was out of town. The last time I got it back the next day. It is nice that the shop is really close and they know me well over there.
My old Pfaff went 15 years without a tuneup-cleaning. It ran great. Once I realized how good it was for the machine I think I took it every 18 mos or so. I had to travel only 10 miles for that one and it was usually an overnight cause the repairman traveled to the shop for a day to do all the repairs.