I think the comment that sewing machines are like cars is a good one. Do you take your car in for a check-up? I don't. I change my oil and such but never take the car in unless it gives me problems. The car has 150,000 miles on it and is going strong. My little machine is a cheapie Brother from Walmart. It is ages old and has made several quilts, Halloween costumes, prom dress and patched a zillion pairs of jeans. I clean it, but it has never been "serviced".
I think you have to do what you feel safe with and what you can afford.
