My wife and I were on the first Fantasea cruise, and we are signed up again for the next one as well. I promise you will love it -- we haven't had that much fun in years. For starters, we have cruised on the Miracle 3 times, and it is a great ship. And while you say it is a smaller ship, that is only in comparison to the megaships that have been launching in the last few years. There were 2,300 people on the ship, and it was a great crowd. No way does it feel like a small ship. And the people from Bare Necessities did a fantastic job as well, so it made the trip really enjoyable.
They announced the average age of the passengers during the cruise, and if I remember correctly, it was 54 or 56. My personal observation was that probably 3/4 of the passengers were within 10 years of that age. But the vibe was definitely younger than the calendar age. Since the group consisted entirely of nudists, there is a much higher level of body acceptance than in any similar aged crowd of clothed people, and that includes acceptance of the aging process. Just about all of these people think like they were still 40. To this crowd, age doesn't matter.
And at the Fantasy Fest, there is a similar feeling everywhere you look. Age is never an issue there. I took lots of pictures there, and you can see them by opening this link: Fantasy Fest 2009 Photo Gallery by jgb911 at pbase.com
If you look closely at the photos, you will notice that while the clothed crowd in the background consists of people of all ages, the majority of the nearly naked, body painted people are over 40. They do not act old, and you don't perceive them that way. In one of the pictures, you will even see an octogenarian with a walker leading a conga line up the middle of Duval Street!
I hope this gives you a vetter feel for what the cruise will be like. More importantly, I hope it helps you decide to sign up to go along!! And if you do decide to go, please email me so we can meet on the ship.