I don't remember if you are sloop or ketch rigged, but I know on a ketch, I can't justify it. As far as coolant, I use the standard 50/50 mix from the auto parts store. Nothing has overheated yet.
My previous mechanic did mention issues he'd seen with internal rust and using tap water, and suggested poor coolant (in Florida, no need really for antifreeze). I've stick with 50/50 and City water (I wouldn't use well water here).