Synthetic oil worth it? 18k hour yamaha generator says no.

I had a pair of mercruiser 454 marine engines in a commercial fishing boat new in 1989. Other fishermen running 454's were having to replace their cams after 2 years. I set mine up from the git-go with pre/post lube oil pumps and Amzoil after the rings were seated. From '89 to '98 when I sold it, I never replaced the cams or had any sign of cam wear. I am a believer.