This might seem silly to some, but I think throwing a bit of flavour text at signature buildings so when unlocked they are presented to the player as;
"We have received a planning proposal for a major development within the city. This signature building requires discretionary city approval to be built."
**[APPROVE] ** [REJECT]
would be really nice bit of easy immersion for the game. As exciting* as the world of statutory planning is, I feel re-framing signature buildings this way moves signature buildings further away from "nice things to unlock in a video game" to "important decision I, the mayor [the player], am making about the direction of my growing city."