-Dole pineapple plantation (I didn't take the train ride but enjoyed making a stop there and the pineapple ice cream)
-Have to admit I never went to the Polynesian culture center, having been to Oahu twice. But I enjoyed the drive to get there and making multiple stops along the way in different parks.
Two things to keep in mind:
1. visit Hawaii not only for scenery also for activities such as snookling, surfing, etc.
2. Many parks are not very well marked and can be easily missed. They did that on purpose.
3. I also enjoyed the smaller towns/villages off the beaten path, away from the tourist traps.