Yes, the game is all about decision-making. That's what I find challenging. It also allows for differences in player style. There is absolutely no one right way to play. You can take from the game what works for you and your city. There are lots of choices.
In thinking about useful items, such as PPs, it's all about where and when you want to use them. They are still useful if used now, or later. It is driven, too, by what chapter you are in and how many chapters ahead of you are going to also benefit from using them. Also, how easily obtainable an item is will affect it's use. If I had 100 PPs and knew I could get more without too much effort whenever I ran out, there would be no issue. As I see it now, PPs are obtainable, but they don't grow on trees. For example, work hard to get a fire phoenix to level 9 or 10 to get 1 portal profit every 48 hours.
I've been playing 9 months. Except for chapter 1 which was quite easy, in early chapters I always seemed to be needing goods, supplies, KP, coins.....everything. I believe this is why I now feel the need to have more than enough of everything. Comfort level. I'd like to have a devil may care attitude. You know - what the heck - it's there, use it - there will always be more down the line....... Um....I'm not there yet