I think you did the right thing. Not only are we each ambassadors for our sport but your boat becomes an extension of who you are and what you stand for. That you turned down the offer for the reasons you stated shows more of your character than anything you could put on the sails. There's a big difference between what you might enjoy alone or among friends and what should be displayed on a 33' sailing billboard. I also detest the people who stole & modified the Calvin & Hobbes image that you always see in the back window of pickup trucks. That one is always fun to explain to the kids. I think a well produced DVD or a Powerpoint presentation would go far in getting additional sponsorship that your comfortable with. Show it to every business you see - you might be surprised that a lot of business owners would buy sponsorship more to help you out than expect a serious return on their promo.
Good Luck,