What does the Upgrade Star Rank event pay?

The Upgrade Star Rank event rewards you for raising your dragons' Star Rank (by spending their Relics). Each star gained gives points that push the event tiers.

It's an excellent moment to cross a tier you were aiming at anyway, because:

• Star Rank is permanent (it never resets) — so it's already a good investment in itself.
• The event hands you bonus rewards (keys, Cores, gold) on top of an upgrade you were going to make.

Strategy: stockpile Relics on one or two key dragons while no event is running, then trigger the star upgrades during this event. You bank the permanent power and the tiers. Prioritize tiers that unlock a big effect (e.g. 6★ to switch on the Panic engine) or your Legendaries (+20% stats per star).