The celebrations themselves are fine. I think the problem is that they're really the only reason to pick a specific government, so like the difference between Oligarchy and Despotism is just... very little. Maybe when you play we'll get a different feeling, but especially since the government only applies to when you're in a celebration, it just doesn't feel like it's that big of a bonus.
I think perhaps if they had some government-specific policy cards at least, that might give you a bit more flavor. Even just like a "Oligarchic Legacy" option where you can slot in a policy card that's like 1/2 as powerful as the celebration bonus, so that at least you always have that available. Something that gives your government a reason outside of just the celebration bonus.