They're still somewhat useful to pull on threads with, though admittedly yes, not so much on the main ones. Selecting a hobby hashtag and searching might find 10% of that content, but you'll find a few people posting about it -- read their posts and you'll find the people they're interacting with about those hobbies.
It sort of brings you back to the webrings days of the internet, when everyone knew that search would only turn up so much, but site to site networking let you actually feel like you were on an adventure around the Internet. Remember when we called it "surfing"? Frankly I miss those days of finding cool content buried away where I might be the first person I knew to discover something, and friends would have things to unearth for me. It does take a lower time preference, but the rewards are worth it if you ask me.
Instead, the modern web is the same 20 sites everyone uses because they're SEO'ed to shit and it's whatever the deep state told them to write about or at least promote anyway. Closest you get to the old feel is Marginalia.nu.
We can certainly also write #Nostr code to mimic this modern crap if it's really how we get people to stick around long enough to enjoy the space. But it's worth remembering that most of what it's actually doing is filtering OUT what people have to say. #MyTwoSats