I'm certain most aren't talking on Area Freq's at unmarked strips however they are certainly listening, myself included. I used to transmit rolling calls from mine when I first started flying & only ever got one reply from a Cathay Pacific at a FL overhead advising that I shouldn't be a problem for him. Over the years I simply dispensed with it & use my eyes (& still my ears) now.
Last weekend a group of 12 aircraft flew to a farm strip just outside of Tamworth & we all agreed before departing that we would communicate on MULTICOM. It worked well & Brisbane & everyone else (except for the other NW airfields using 126.70) weren't bothered by us. Just made sense to all involved & we did discuss the fact it was not what was required.
I am organising a fly in to a private unmarked on charts strip shortly & I have advised everyone to use 126.70. Why? Expecting maybe 40 or 50 AC to arrive during a 1 hour period. Imagine the congestion on Area Frequency during that period. Certainly no doubt 90% of them will have dual monitoring anyway & be listening still on area.
Just seems to be common sense to me but maybe I (& others) have it wrong