Is it bad to wear reading glasses a lot if you have good vision?

No.... ..But it may cause undue strain. Up until the 40s, the eyes can normally focus for near work. By the late 40s, near focus becomes difficult. Reading glasses are essentially magnifiers that help you focus up close. If you can focus up close on your own, there is no reason to use readers, and they can give you headaches. There is no danger, however, in using them.
Probably not. You wear reading glasses for close up and intermediate reading when the lens of the eye becomes stiffer with aging and will not focus as previous. Beyond those distances of say 1-3 feet, one cannot see out of the readers and thus not damage the eyes. It would cause undue strain and discomfort to try to look through them and you just will not. Not a worry.