I tend to call my break even costs to be 10 visits per membership year with at least 2 of those visits been a good couple of hours. At 10 visits (and they need to be proper visits, not just 5 minutes to go to the loo between connecting flights) it brings the cost down to around $50 per visit.
Whilst that does make it an expensive beer / G&T it's the non food and drink things which make all the difference (eg been able to take a shower before an o'night flight, or having a quiet place to work).
Of course a visit where I'd have lounge access anyway (eg when I'm flying J) doesn't actually count towards my 10.
Beyond 10 visits every visit is a bonus.
I guess a big problem is lounge access is like a drug... In theory you can quit it anytime you like and spend a couple of hours down in the terminal, however when you actually do all you can think about is what you need to do to get back into a lounge / how great your next flight which allows lounge access will be. QF knows it and they know that if they do a price rise, the vast majority (myself included) will cough and moan to the cows come home, vow how bad QF is, but then pull out the trusty CC come lounge renewal time.