Regarding having much older units that aren't worth fixing I might be very hesitant to make that conclusion as older door closers are practically impossible to get your hands on.
Advantage of repairing these whole door closers is that while they provided decades of service initially once we rebuild them they will provide an additional several decades of service. The only time that you may elect to upgrade to a modern closer is when you have an obligation to meet reduced opening force for ADA.
That stuff from mid-century is most absolutely worth repairing You should send us photographs and I'll price it up for you.