I've got some numbers, took longer than I'd have liked because of ISP issues. Each period is about a day, give or take.

With the default TTL, my unbound server saw 54,087 total requests, 17,022 got a cache hit, 37,065 a cache miss. So a 31.5% cache hit rate.

With clamping it saw 56,258 requests, 30,761 were hits, 25,497 misses. A 54.7% cache hit rate.

And the important thing, and the most "unscientific", I didn't encounter any issues with stale DNS results. In that everything still seemed to work and I didn't get random error pages while browsing or such.

I'm kinda surprised the total query counts were so close, I would have assumed a longer TTL would also cause clients to cache results for longer, making less requests (Though e.g. Firefox actually caps TTL to 600 seconds or so). My working idea is that for things like e.g. YouTube video, instead of using static hostnames and rotating out IPs, they're doing the opposite and keeping the addresses fixed but changing the domain names, effectively cache-busting DNS.