That's exactly it, Mike. Fact is, the majority of Vintage horns out there on the market are not in good tack - they haven't been kept up to speed. They may be closet queens, they may be retired school band instruments, they may just have had 5 or so owners all of whom only were willing or able to pay for what an sax acquaintance of mine dubs " M*A*S*H* Repairs" (just patch 'em up well enough, and send 'em back out into the field). MOST older saxes sold fit somewhere in here.A valid point worth making and well taken, @JayeNM!
My sax is almost 60 years old (early 1960's). So by most definitions, it's a 'late vintage'. I think you're right that if a sax (even from the 1920's or earlier) has been well-maintained, there's no reason in principle why it should require any more maintenance than a modern sax. I know absolutely nothing about sax construction/mechanics but just perhaps (due to their construction) older saxes may need more frequent adjustment than newer saxes. I may be completely wrong!
I deliberately bought my 1960's sax through a small shop that makes most of its money on maintenance and repair. They only buy in good quality 2nd hand saxes and they thoroughly check them out and make any necessary repairs/adjustments before selling them on. So their saxes are not as cheap as on E-bay but buyers like me can have confidence that they're buying a good quality, refurbished, well-adjusted and playable sax.
I suspect that the 'nightmare scenario' for some sax players is that they spot a'vintage sax bargain' on (just for example) E-Bay that perhaps initially sounds OK (or not) and that soon requires major maintenance/repair to compensate for a lack of maintenance (or plain defects) in the past. I hope @jbtsax will chip in on this.