Hyperium, the second tier strategic resource is used for city upgrades, but all of the upgrades which require it also require the third (and last) tier of strategic resource as well.

This makes hyperium quite useless, since you can't utilize it until after the third tidefall, at which point it's not a constraint since you'll be sitting on a huge stockpile of it due to extracting it for an entire tidefall cycle without any spending. (And that's if the game hasn't already ended by then!)