I bet with all of his other senses being heightened, the sounds/vibrations/wind/noises... must be pretty exhilerating! My younger sister (40yrs) gradually started to go blind around age 10 and has been a couple decades, now. Earlier this year, while walking through some grass towards the cabin, I took her hand and said "let's run!". She was at first hesitant, not thinking she could do it. I just said "Nope - we're doing it!". She was laughing and gigling like a little school girl!
I absolutely don't think that you WON'T sell the boat with bottom paint on it, but you will limit your potential buyers. Some won't even call if they see bottom paint as the assumption (to them) is that it's been a saltie it's whole life. Right or wrong, it's the way it is. On the other hand, an un-painted boat that has seen primarily fresh water is more of a rarity and will command a higher price. In my opinion, with the way you are using the boat, I don't see a need to paint it.