For food service, specifically waiting tables - how much of the tip is because of effort and better service - and how much is due to the attractiveness and general demographic characteristics of the server?

Good question. I would say mostly the former. I imagine you might say the latter.

I personally top out at 20% no matter what. If the service is lousy I’ll go lower. When servers/bartenders are comping me then I know they get it and will up my percentage.

I guess carrying around a large rack takes more effort than a small one.