I don't suppose collecting sewing machines is much different than the machines guys collect. My late Dad had tons of motors - wouldn't give up any of them, but only used a fraction of them.
My sister has 3 machines now - one is a serger. However, she has a business selling high quality doll clothing. Each machine is set up differently so that she doesn't have to keep resetting stuff. So, instead of sewing year round, she now gets all her stock done in about 3-4 months so that she can focus on other stuff like fishing and gardening. :)