I think I've been to an airport lounge once and a train travel first class lounge once. I have heard of Priority Pass (they advertise in UK in flight magazines), but for the limited air travel that I normally do (two or three short return flights a year) it didn't seem worth it.
Airport lounge was BA in London, about 7 years ago, was breakfast time and had a decent cold breakfast offering plus soft drinks, coffee. Plus WiFi, power, newspapers, space, tables. I would not necessarily expect a commercially-run lounge to have more than free soft drinks, fruit and snacks (if the airline provides the lounge for business/first they can build the cost into the plane ticket/run it at cost, if the lounge is a standalone entity it has to be profitable by itself). But with normal airport food prices, and the lack of space, WiFi issues and noise, access to a lounge even for the basics could be well worth having.
Train lounge was Virgin Trains in London. Lounge was full of people, quite noisy. Free soft drinks and very basic snacks only, I mean can of orange juice and small packet of pretzels was about it. Tables with power and free WiFi but too busy. I had booked a first class train ticket as it was the cheapest option (UK train ticket pricing is sometimes quite nonsensical), went to the lounge to see what it was like, would not make a particular effort/pay to go back there again.
Hopefully Priority Pass airport lounges are a bit closer to BA standards than the train ones...