Buying a bit bigger than you think you need, and smaller than the max you can just barely afford strikes me as a good balance. I'm happier buying parts for my A30, and happier working on the big 45'+ powerboats with more elbow room when someone else buys the parts and pays for fuel/moorage.
I wouldn't want a 60' boat for example, for my needs it's just too much, especially when it comes to cleaning!. However a 36' feels just a bit too big for me, including extrapolating extra space for things I don't own but may want, and including space for a partner down the road if needed. Everyone's needs may be different, but general guidlines could apply.
The A30 I own, is just right for me now, but I suspect I'll want more room later, and then I'll have a nicely outfitted boat for someone else to enjoy the fruits of my labor.
EDIT: Also, you have inspired me to add some granite to my A30, I used to fabricate and install granite countertops, and there's one granite that would be just perfect, it's a strange mix of cream, orange, black and translucent, the kind of look no synthetic has.
I'm keeping my eye out for a small piece to do my galley with if I don't go full synthetic.
Interesting story on our granite installation a few years ago.... a quote for replacing the formica was $4500 in just the galley. Instead, a likewise "burnt orange / cream / black" mixture, (which really added a lot of zip), for the galley AND both heads came to $2500. I ended up having to install it as they were gouging the teak all around the granite, but nevertheless, it was much better than the formica and cost a fraction as much. Also it didn't create any list or imbalance to the boat, perhaps because the aft head offset the galley, and the bow head was more centralized.
When you liveaboard, and especially if you are married, it is some of these little touches that appease the "nest building" portion of us.