I thought I've answer my own question having just flown on QF93 and QF18. As so happened, I signed up to an ANZ credit card with a large point sign-up bonus therefore I had enough points to successfully upgrade on both flights. As much as I tried to sleep on the flight over, I wasn't able to and ended up tossing and turning in the skybed mk2 until I gave up and watched TV. I arrived in LAX, flew to LAS and then grabbed my rental Mustang and headed off to Hoover Dam (ran on adrenaline until about 9pm that night and then slept very well!)
I also upgraded on QF18 and that was a much better use of points as it gave you access to the LAX J lounge, which was far nicer than sitting at the gate for 2hrs during the layover, and I did manage to sleep on the LAX-SYD leg.
In summary, the upgrade on QF93 from PE to J probably wasn't that useful as I didn't sleep anyway. But QF18 was well worth it!