Many vintage machines have crazing on the shellac and other paint issues due to the heat/cold of attics, basements, garages etc. So, the climate does effect them long term. However, like you, space is a premium and heating and cooling spaces just for machines is hard to rationalize for most people. For me, the best way I deal with space and heating/cooling concerns is to keep any machine with nylon/plastic gears or parts in my house. They're either in a closet or set up in a room. Parts machines are kept in my unheated or cooled garage. I don't care if the finish of the machine is effected. Any parts like bobbin winder tires and belts that are also effected by the climate are usually removed. Similarly, machines that I treasure are all kept inside. Vintage machines have survived in unheated spaces and will continue to do so, but generally the ones in the best condition have been stored in the home. I think you're fine if your machines are kept out of the elements, away from moisture and are typically kept at a decent temp. I don't think a few cold spells like you describe will hurt them. I would not let any computerized machines freeze, though. I think your machines have a nicer life than most!