Maybe it would make sense for credit cards to have gold and then an additional lounge pass system, where you get (say) 10 passes per year. This is quite similar to a number of airport schemes, or even on some FFPs giving lounge pass gifts you can give to non-status friends.
Naturally, I say this coming from a night/stay base qualification - there is no chance I would hit 18k spend in a year, even if I have sometimes hit the nightly, unless Conrad and WA start to appear in my work booking tool!

To be honest, I would not expect them to segregate credit cards so they would probably end up introducing such a system to diamond carte-blance, where we get X passes upon achieving diamond and then Y more at future milestones; Only the reserve gets unlimited access. I would not be necessarily against it, lounges are so full these days if it means going less but having a better experience I see a benefit.

The flip side is, what does this do to executive rooms? I usually get an upgrade to exec because it costs the hotel nothing to upgrade me; It is a placebo upgrade in many ways for diamond which allows them to oversell standard rooms to people whom would not otherwise stay.