Excluding major weather events like hurricanes, the organizer should still host the event. As you said, contacting everyone is about impossible and predicting the weather is still not an exact science and could change. Trying to reschedule the event at that time of the year would be just about impossible given all the other regattas going on (in our area anyway).

I don't think the organizer should offer 'money back' due to weather. That could start a landslide and leave them unable to cover known, and already incured, expenses (the food, shirts, beer, etc. have already been purchased).

Somebody refuse to register until they know they'll race? Well, it says right (insert the "here") that open registration is from 8am to 9am Saturday morning. 9am should be the deadline for them to make up their mind. Personally, I don't have any problems with rules as long as I understand them - I imagine most folks are that way.

Entertainment? Spend that saved boat fuel money on a little extra beer - we're pretty good at entertaining ourselves.