Count FL,
There's a lot to see in New Guinea. On the outskirts of Port Moresby is the end of the Kokoda Trail where Australian troops exited to retake the city. There are also some Australian Coast Watcher outposts preserved. There are still some plane wreckages, both Japanese & Allied in the jungle areas.
Rabaul has Admiral Yammamoto's headquarters and caverns dug into the mountainsides along the harbor to hide barges. Thousands of natives died doing the digging for the Japanese under horrible conditions. Several of the barges are still there.
Bougainville island has several spots to see.
In Honiara, Guadacanal there are still underwater wrecks of ships & planes to be explored by scuba or snorkel.
Midway is an excellent stop for WWII buildings & equipment (as well as a few hundred thousand albatross known as Gooney Birds.)
Jim