There are heaps of Qantas Club and Virgin Lounge passes trading hands in the OzB Classifies all the time, and they seem to start at $50 for long expiry and come down from there. No one seems willing to part with a pass for less than $30, even if it is about to expire (seems crazy to knock back an offer then have the pass simply expire) I've been a regular user of both QC and VL over a number of years, but I don't see there is $50 of value in there, unless perhaps you have a very long wait for your flight.
Yes, I can knock back quite a few drinks in an hour (and have) and you could say it is good value for that, but the food options in both lounges are pretty poor (with no options to buy anything more than the buffet on offer) and personally I'd rather spend $50 on food and drinks inside the airport, with the fare offered these days improving considerably compared to a few years back…
So, if you a someone who buys lounge access, why do you? And what makes you feel it is worth $50?
ToM
Sometimes I will buy them as birthday gifts for friends who are travelling. I agree, they're not the best value at $40 (which is the max I'll usually pay), however they tend to make a very 'unique' gift to the occasional traveler who has never been to a lounge before. They are usually quite surprised and excited to get one. They tend to appreciate the experience more than a frequent business traveler.
I usually ensure they are departing from an airport which has a decent lounge before I buy a pass.
I would buy a QF pass for myself if I had a flight departing from a nice Qantas International lounge - thinking London, Singapore, Hong Kong or Brisbane International currently.