As a car person, a sewer/quilter and the wife of a mechanical type, I have to chime in on this. There are a lot of factors involved in engine life and it's not always how much it's used. A lot has to do with maintenance. Good maintenance on car can make the difference between 80,000 trouble free miles and 150,000. That being said, there are also lemons that give you trouble no matter what you do.
I agree with Scraplady that mechanical devices need to be used. We have had several vintage cars over the years and if they aren't started and run, preferably actually driven, they will give you trouble. My husband claims that a mechanical engine (as in pre computerized controls) will break faster if left in the garage and never driven than it will if it's used and cared for.
I don't really worry about "cost effectiveness" with my sewing/quilting. I could most always buy something cheaper than I could make it. Would it be a beautiful, as unique, as well made? No, probably not. But it would be more "cost effective". I'll go for the beauty, originality and true value of a hand made quilt any day over a mass produced one.