My wife and I flew United in First SFO
and return in October. We used a corporate travel agent and had unlimited flexibility with our travel dates, but the travel agent had no luck finding upgrades with mileage for us. He said United is very stingy these days with upgrades to Hawaii.
So, we paid the First Class fare (the agent found us a very good fare given our flexibility in travel dates). For my money, and this is just one person's opinion (but my wife agrees), the extra money was worth it, not necessarily for the food and extra room in First Class, but simply so we weren't crammed into Coach with all the aggravations that entails. We really don't think of ourselves as snobs, but we got a good deal on the First Class fare and figured, what the hell, it's worth it just not to be stuck in Coach.
The service on the flights was very nice. Food was tasty and ample (I had a hard time eating all of it) and the flight attendants were friendly and accommodating. So, for my money, it was worth it even if First on United Hawaii flights is not what one would find on many comparable international flights.