I generally keep stuff for a long time, and won't buy anything unless I know I'd be happy with it forever if I kept it that long. Everything is for sale for the right price, but I'd be perfectly happy if I had my current boat 'till I kick the bucket. If someone came along with the money I'd want for it, great... It would be gone and I'd probably end up buying the same model boat but a couple years newer with composite stringers so no worries about a stringer job in the next 10-20 years. My boat is an '89, my truck an '86, my car a '68 and my bike a '71. I see no reason to sell any of them to buy a newer replacement. Most people are in a race to get the next newest toy, but to each his own. If what I have does what I need, I'm happy. If it doesn't, usually it's just a matter of adding horsepower (or in the case of the boat, tower and ballast), which makes for fun winter projects.
Your boat should have another 1000 hours before you have to worry about anything major, and even then you're only talking a couple thousand to rebuild the engine, trans maybe $500, not sure on a vdrive but maybe a bit more than a trans. If it does what you need and you're happy with it, keep it until you're not getting what you want from it. Sounds like you've put a fair amount of time and money into it to make it yours so I'd assume you're pretty happy with it. It's a composite stringer vdrive so should hold value well since it's past the initial depreciation.
As for the work I put into my boat or other toys to improve them or make them mine, I don't let that factor into whether I sell something or not. Sunk costs and whatnot. I do all the work on my toys because I was taught to never pay someone for something you can do yourself. I view it as money saved, not so much time invested. I know things are done right and to my liking, and if I do sell I have more margin before I take a loss since that time I spent working on the boat i's at times when I wouldn't have been doing anything particularly constructive.