$100/month/ft sounds like a decent rule of thumb. I like round numbers.
As for the question of minimalism and all that, our tastes are very modest. We don't eat out six nights per week, we don't wear fancy clothes or drive fancy cars. In contemplating this boat, we want big for its own sake...We have seven kids and the grandkids are coming on strong so there is every reason to expect a steady stream of them coming for visits. And we want as much boat as possible for our planned Atlantic crossings.