1990 Civic LX - valve clatter noise getting worse

I posted here a couple months back about my 1990 Civic LX having a loud clattering noise when first starting cold and the noise easing up as the engine warmed up. Advice I got at the time was to have the valves adjusted. I hadn't had that done in a long time and it did help, but the noise persisted.

Car now has 291,000+ miles and the noise is there even during the summer, when it's warm. It still goes away after about 10 minutes of driving.

Any idea what this is? How worried should I be? I'm between jobs, buying a house, don't really want any more big car expenses. I just put $1000 into brakes and front end. Guy at the shop said would go another 50K at least, but I wonder.

Thanks!