Two happiest days of boat ownership - the day you buy and the day you sell.
Went through the same process when we bought our vacation house. We are 2 min from a lake in N GA, not on the lake (If we were on the lake, we would have a boat). We can rent a ski boat 6 times a year just for the cost of the slip rental alone. It was a slam dunk decision for us - no insurance, no maintenance, and someone else cleans the boat.
Are you on the water? If not, then the spontaneity fantasy is gone.
Definitely rent the first year. See how often you go to the house - the first year & second is the high water mark. Then see how often you rent a boat.
By the way you will need one pinball machine, just one to get your fix in. I bought a cocktail machine and it worked out perfectly.