Only 500 mating cycles? This makes me wonder if 3 year scope warranty covers BNC connectors.
Have you ever worn one out? I haven't, and I have multiple scopes that are over 30 years old. A portable scope that is used in the field and gets packed and unpacked every day could have an issue but in most cases I wouldn't be worried about it.
I have had flaky BNCs on some test equipment. So yes, it is possible to wear BNCs. But age doesn't matter; the number of mating cycles does. I make it a habit of not disconnecting probes when I don't have to.
I've also experienced worn PCI slots (which are typically rated for 30 mating cycles or so) which meant throwing the motherboard away (this was in a PC used for testing boards so it did see quite a lot of mating cycles).