Everyone needs to put this in the context of their own lifestyle. What is your primary insurance? Do you need a secondary and so on.
Talking about the medical coverage, USA-WS offers secondary medical coverage. It kicks in only after the Medical coverage from my Boater's Insurance is exhausted. The Boat-US basic boat policy includes $5,000 medical coverage (per person per incident). Family members receive $25,000 of medical coverage (per person per incident). See attachment. These limits can be raised for a small increase in premium.
If you are injured skiing, don't forget about filing through your boat policy. I don't see a deductible on my policy and I am no expert. Check with your agent.