I have used CHUNKS to represent upgrades to a home. I ran a spelljammer style space opera game with my home group, their ship became dear to them. They invested time and resources to change their old junker into a sleek warship.
Things to consider for upgrades; Hull (defense), sails (speed/ maneuverability), armaments (firepower), magical enhancements, aesthetic changes (make it terrifying to behold, or a beacon of hope), mess hall (food could give temporary bonuses when prepared), hiring crew (navigators, sailors, chef, on ship merchant, gunmen, doctor, heck even butlers.
Another way to go could be inheriting a run down mansion, and they could renovate rooms or places surrounding the property to serve functions; barracks, stable, medical facilities, kitchen, laboratory, war room, fortifications, traps, hidden passages (a personal favorite), training grounds, an exotic herb garden, a mote, etc. (each of which would give them access to some kind of ability or boon when they return home)
I hope this helps to get the gears turning and remember, if they earned it they have to keep it. Make something too nice and folks might just get jealous enough to try and take it for themselves, which could be an adventure in and of itself!