Here's a rundown of how Golden Tickets work in SimCity BuildIt.
Save them up at least until the City League
Golden Tickets are valuable items right up there with Crystal Keys, so I'd recommend saving them for the moments when you really want to lock down a top finish. In the City League and below, you can still aim for the top spots without using any.
Above the Metropolis League, Golden Tickets are basically essential
The image shows the leaderboard for the Megalopolis League, and climbing into the top ranks is tough enough that Golden Tickets are pretty much a must. To break into the "Prize" tier or above in particular, it looks like you basically have to spend all 15 of them. That said, I've had leagues where I burned through all 15 and still ended up stuck at the "Token Prize" tier. Which players and assignments you get matched against is random, so there's a luck factor at play too.
You can use up to 15 Golden Tickets per league
You can use up to 15 tickets in a single league. Spending money won't push that cap any higher.
Golden Tickets can't be bought with SimCash
You can't buy Golden Tickets with SimCash, the paid in-app currency. Heads up: while a league is in progress, leveling up is the only way to add to your stash. In the higher leagues, you'll end up spending the tickets you've steadily built up from level-ups and rewards.
Joining a new Season nets you 10 tickets
The Mayor's Contest runs limited-time events called Seasons, where you can earn special buildings. When you join a new Season you do get bumped back to the Neighborhood League, but you receive 10 Golden Tickets, so you can stock up for the next league.
