I focused a lot of my award-travel resources on the South Pacific in the last decade or so, using the stopover rules to the hilt and spending countless hours trying to nail down the perfect trip, sometimes against what agents on the phone said was possible or permissable.
For me the two "heroes" were CO and their Micronesia network, and NZ using UA miles, in both cases for regional awards (either Australia or Asia to Micronesia or S. Pacific) at 20-25K. A typical award ticket might go something like BNE-AKL-PPT (stop)-RAR (stop)-AKL-BNE on NZ, or the "illegal" one I did of AKL-RAR(stop)-NAN (stop)-AKL. On CO I once got MNL-GUM-MAJ (stop)-GUM-YAP(stop)-GUM-MNL via computer at 25K even though the agent swore up and down they couldn't do it. On another trip is was MNL-GUM-KSA (stop)-PNI(stop)-GUM-MNL on the island hopper. All those flights would be very expensive as paid tickets.
Some of the islands indeed are under-touristed and great experiences if you can get the booking somehow. Am a big fan of the Cook Islands, and they're a much cheaper alternative to Tahiti. Hopefully "Survivor" didn't ruin Aitutaki. Western Samoa is really beautiful. Fiji is more touristed and many people go for the "castaway" experience in the Mamanucas or Yasawas, which is a bit narrowly focused. In Micronesia, Pohnpei is really beautiful, has Nan Madol (and you can drink kava at night) and might have 40-100 tourists at a time. Yap for Yap Day was quite an experience, especially seeing all those dancers try to maintain composure as a fierce rainstorm blew through because all the chiefs were watching. Palau has unique scenic beauty. Majuro and the Marshalls are really, really unique and might not exist in 75 years due to global warming.
There's a midlevel with the likes of New Caledonia, Kiribati, Nauru and a few others not heavily serviced that'd be nice to see someday, and I wish I could have gotten to see Tonga. A big money-saving rule of thumb for many places, like the Cooks, is to get a fan room rather than an AC room, as you probably don't need the AC and the cost savings can be substantial.