Does it really matter who I side with when it comes to structure development? I've been reluctant on continuing development quests until I can figure out if this is soley for unlocking voice lines (which i feel i've unlocked only 2 for Kiyo despite catering the island based on her interests for 6 structures) or if it holds some value in the end. I want to diversify my structural options but I'm not sure if that will affect the outcome.
Things I'm sure about:
1. Voice Lines and Cutscenes are exclusive
2. You gain MP on re-runs
Like you said, rebuilding is just to gain more MPs. I just finished the island a bit ago and got Scathach (for now). When you finish the island any way, I went Tamamo heavy, all the summon ticket quests appear. 5 in total I think. I was also worried that once you pick one the rest would go away until you rebuild, but nope. I was able to do all the summon ticket quests. So it does seem that rebuilding is strictly for MP and dialogue and a ton more wasted materials lol
Your decisions in developmental quests are purely aesthetic in the end. There are no different 'endings' if you indulge certain characters exclusively, if that's what you're worried about.
Also, the ones who suggested the idea will provide the line once you complete their plan. In the case of Kiyohime, her idea will usually be shared with Tamamo. So if you follow their idea, it will either be Kiyohime OR Tamamo that will give their regards to you.
Lines and cutscenes can be found in the internet so you won't be bothered to reset your island. Just farm for the shop, mate.
