Whether it's worth it would also depend on whether your destination was Australia or NZ. If going to New Zealand, then most people would say extra miles plus extra trans-Tasman connection to fly UA F via SYD would definitely not be worth it, unless you also want to stopover in Australia.

If going to Aus, then it becomes a harder decision, since the NZ option will involve extra stops/travel time, plus a trans-Tasman connection. Not having flown UA F, but having been in UA biz on quite a few flights, there's absolutely no way I'd spend any more points for the UA experience, unless I didn't have a choice. You're basically getting a pretty poor-quality business class service but in a pretty good F seat.