Does replacing cross overs in 25 year old speakers make a difference? Assuming they used open air cores and polypropylene caps. I understand those caps don't change in value over time.
The proper design and function of a speaker's crossover is far more important than the quality (or price) of crossover components.
In answer to your questions:
Yes, any inductor coil (air core or steel/iron core) and polypropylene (or other plastic) caps keep their values over time.
Some,
but not all, electrolytic caps have been known to leak and/or fail as they age. I emphasized the words but not all, because only some electrolytic caps (non-polar electrolytic, NPE) do this. Read about the Capacitor Plague, where some caps, made in Taiwan or China during the late 1990s and early 2000s, failed frequently.
https://en.wikipedia.org/wiki/Capacitor_plague
It can be easy to tell if a NPE cap has failed (but not always), but the only way to know if a NPE cap has drifted out of its specified value is to remove it and measure it's capacitance. Although people on the internet make broad generalizations about NPE caps always leaking or failing, it's really not possible to generalize about this.
I've read of tests that show statically random listening results, yet there are web pages that list capacitor performance like describing fine wines. I understand the argument of manufactures using cheaper components to balance cost. Is any of it measurable?
It's rarely, if ever, measurable. Avoid those web pages that "list capacitor performance like describing fine wines". I think they're full of nonsense. Most wine critics do understand the importance of blind taste tests – but not the guy who makes up that fiction about how different capacitors alter the sound quality of speakers.
Really how old are my speakers in "dog years"? And how about those cheap molex spade connectors (as compared to the gold plated posts on the outside of the box) that tend to connect all the internals
Impossible to generalize. Some speakers hold up well, others need to be retired as they age, and some were dogs when they were brand new and should be taken to the pound.
As long as those "cheap molex spade connectors" conduct electricity they're fine. But you can find plenty of fairly inexpensive gold-plated brass connectors and replace those old ones. They'll look nice, but don't expect any changes in sound quality.