I would pay to have a pro-grade (Nikon, Canon, Leica Pentax, Rolleiflex) camera that I used regularly serviced, but doubt if I would for the consumer S.L.R. cameras of the seventies and eighties whose designers and engineers when selecting the materials to make them out of and the engineering tolerances they would be manufactured to when starting the project never actually envisaged them to have a service life forty or more years. The fact is that the majority of these cameras have never had any maintenance, are worn out, and have reached the end of their service life.
That hasn't been my experience of it at all. Many of these cameras have hardly been used, luxury buys just occasionally used for holidays and family get togethers, then chucked in a cupboard. Obviously certain pro spec cameras have had heavy use, but it's pretty obvious when cameras have been used like this, because they have all the battle scars of heavy use. I'm frequently amazed at the condition of the cameras I pick up. Film users always had to be cost and time conscious, so unless used by a Pro many of these cameras have hardly been used in reality. I have 6x9 folders, 50's, 60's and 70's era cameras that are still pristine. About the only issues some have are foam light seals degrading, which is easily fixed.
Ebay is chock full of cameras still in excellent condition, as long as they have been stored sensibly, which is always the thing I look out for, the give away is usually fungus in a lens. Of course it depends on where you live, in the UK, in a temperate climate, cameras will last a lot longer than in a tropical environment. I picked up a mint condition Pentax S1a recently, the lens was stuck on it, and the mirror stuck in the up position, I simply opened the back up, freed the lens which was trapped by a stuck lever, then removed the bottom plate and lightly oiled the gears with clock oil, it virtually instantly freed itself, the mirror dropped and it works like new now, all shutter speeds bang on. It had obviously been stored in a dry centrally heated cupboard for many years. A great camera, in great condition restored to mint condition with a bit of thought, it'll probably outlast me. My Pentax 67 on the other hand has had heavy use, it has the scars to prove it, but I knew that when I bought it, but it's still going, you just have to wind on carefully and it works great, I'll use it and enjoy it until it fails, and in due course buy another body for that eventuality.