I played with Caddy a lot in the v1 days and again recently with v2.1. I ended up not sticking with it since there's things I do with nginx that aren't easy to do with Caddy if you don't have extensive Go knowledge. I am tempted to give it an honest go again, though, and see what I/it can do.
As for Caddy advantages, I think it's really just about having a super easy to manage JSON or Caddyfile. In migrating a few of my nginx configs to Caddyfile, I was able to reduce line counts from dozens to 2-3. That's pretty impressive, tbh.
If you've been using nginx forever and have no issues with it...I don't see any valid reasons to move to Caddy.
