I’m OK for short domestic hops in Y - and even more so with QF Economy Plus.
Long domestic eg CBR -DRW or CBR-PER I prefer J
Intermediate domestic eg CBR-ADL, it depends on the deal I get.
International it’s J all the way, but like others not at any cost. We are retired now so have a lot of flexibility on departure dates in both directions. This can often result in savings of over $1500 on fares especially to USA, EU. We also look at departure points within Aus. We live in CBR and it is often significantly cheaper to transit via MEL rather than SYD, even if it necessitates an overnight hotel to permit an early morning departure . Again, we have only had this luxury since retiring. We have also started looking at the options for connections through Asia, but have not done that yet. In terms of what we pay, for us it isn’t a comparison with Y as we re not doing that. Rather we know what typical fares on our airlines of choice are, and jump quickly onto any decent sale fares that emerge.
The other thing we consider is the fly more pay less mentioned by
@CaptJCool upthread. We often fly to DXB to visit Seat Son who lives there. It is usually same price or even cheaper to make this a flight to any port in Europe, with 2x30 day stop overs in DXB plus an optional Asian port stop over in each direction that just fly direct to DXB. When I first found this in 2018, I could not believe it, but we have subsequently done this many times and it is often enough to make the European part of the trip either free or all but free. But again, this requires more time, and was not something we could do when working.
Finally, for the last couple of years I have just paid what I think is a fair price for my J International travel without too many regrets. I have cancer of the “chronically terminal” variety. I am now very aware of my use by date, and there re things I want to do, places I want to go and most of all people I want to see, plus I now don’t have to plan for quite as much aged care as initially thought

, so I am spending what it takes without paying crazy fares. I think $15k return J to USA or Europe is a crazy fare and I won’t pay that - I just look for better deals, including trying to use points.
And as mentioned by
@Forg, the only times I’ve flown F is when I’ve been given operational upgrades $ I don’t think it’s worth the money to buy outright or the points for points upgrades for the incremental value differences between J and F. Unpopular view, I know. As a OWE I get pretty great perks if I stay within One World Alliance.