I agree that it's "each to their own". For those that have a low FF balance (low number of flights and CC earning), then any free flight might look good. The ability to use them is what it's all about.
For those of us with multiple CC's all linked to our QFF account, plus being regular travellers, then the ability to garner large number of FF points means we can be more selective with how we use them.
My wife and I agreed that burning 288K points (4 x 72K) for J upgrades BNE/LAX and LAX/AKL/BNE for us was well worth it. So was burning all her AA points for upgrades to First on our USA domestic flights.
The value of a Skybed for a 13.5 flight on the way over and a 17 hour flight (plus a 100 minute layover in AKL) was outstanding value - not just from our comfort viewpoint, but also how happy we were with each other...brownie points are hard to come by and easy to lose.
Similar for Australian domestic upgrades...I use points generally only for flights in excess of 2 hours (with a couple of recent exceptions). Find me anybody who wouldn't want to fly in J for those sectors, rather than Y.