Premium economy is like domestic first class with foot rests (or in some cases a foot bar). It doesn’t let you lie flat, but it gives you extra room and some upgraded amenities. I don’t think it’s a replacement for business class on ultra long haul flights, but it’s ‘good enough’ flying transatlantic Westbound (day flight) and certainly a whole lot better than coach.
I watch Sydney fares because I have family in the suburbs there, and I’ve been going since I was a kid. In fact my very first international trip was to Australia. I even flew American Airlines the last time they served Sydney — DC10s via Honolulu.