I have full-fat PP (i.e. no entry fee) with one of my credit cards. To date I haven’t used it a great deal since my FF status and choice of airlines/travel class normally guarantees me lounge entry anyway, but I still see it as a useful benefit. For instance, on my upcoming MH flight to London I hope to use it at the T2 arrival lounge (yes, I know MH arrive into T4, but there is no arrival lounge there!). I have used it on a (very) few other occasions. Not something I would be likely to hand over hard cash for as things stand, but if I lost my PP status (highly likely when I retire) I think it would be worthwhile. I have looked at the others, and PP does seem to have the best coverage – a really huge number of lounges. Plus, for those without oneworld status and based such that they fly BA through LHR T5, the advantage (space permitting!) of access to the only pay-in lounge in that terminal.
Incidentally I did look recently at the idea of paying for PP for Senior Offspring. But decided it (not she!) wasn’t worth it. Everything I have seen on here goes to confirm that conclusion!