"the boat is going to have higher maintenance, since the underwater gear still needs to be maintained to a certain degree—through-hulls, plumbing, etc, are still equipment that needs maintenance, even if the boat is not being used for transportation, since if they're not maintained, the boat WILL SINK"
The boat next to me in the marina has sat unattended for three years and has yet to sink. Actually that's an exageration. about two and a half years ago the wind blew in the companionway drop boards and enough rain water to put the hull about two inches below the waterline. I foolishly notified the marina and the owner, reluctantly replaced the drop boards, using that cheap panneling found in most garage conversions, but that's it, no other TLC whatsoever. Fiverglass is prety remarkable stuff. Also, the marine growth on the hull must provide some protection against sinking as thick as it is.