I had an old Toyota pick up with a mechanical cam that went 200k and never had the valve cover off.

Slant 6's were all mechanical cams up until the last one or two years of production.

For a modern high performance street friendly mechanical cam in a traditional v8 platform, I'd say popping the valve covers off for a look-see every 3000-5000 miles is probably a good idea.

The right type of solid cam wouldn't be any noisier than what you're dealing with now.