How much could we benefit from being more laid-back, from openly and deliberately saying "fuck it"? From doing what we actually want to do without regard for what's expected of us?

I would say substantially. LW largely seems to advocate for preference utilitarianism, whereas EA and animal rights subsets of the group often come suspiciously close to deontological "whatever you do care about, here is what you should care about". As a matter of fact, the whole advocacy for consistency in ethics (e.g. "shut up and multiply") can backfire since System 1's values are not necessarily consistent. I'm not suggesting giving up on these attempts, but I guess that many people would benefit from being able to listen to System 1's voice saying "I want to invent a lightsaber" without having System 2 immediately scream "but people in Africa are suffering, and you're just being scope insensitive".