Good advice. In addition, one may want to think of "work done" on the boat as either "maintenance" OR "improvements."
A GPS, a new VHF radio, other navigational tools could be considered improvements over and above basic necessities like a basic VHF. In most cases, because electronics improve so rapidly, there is little to be gained financially. Sometimes new owners prefer basic boat electronics so they can add the electronics THEY prefer. It's like adding the shag rugs YOU like before you sell a house: the new owners may NOT like them at all!
Maintenance includes just about everything else, much like what you pictured. Just because a previous owner neglected your boat doesn't mean that what you put into it means it is any more valuable. For example, neglected seacocks that didn't get exercised and need to be replaced, do not add any value to a boat. Many boats have skippers who do not neglect standing and running rigging, or seacocks or blocks, but don't get premium prices for their boats.
The main differences here are significant FEATURES. For example, there was a post recently where the questioner asked if he could buy a boat in the Caribbean, sail it to Vancouver, and make money! Neglecting the cost of the trip for the moment, my response was that it would be difficult for him to find a boat in the Caribbean that had the diesel heaters so favored by folks in the Pacific Northwest.
So, put aside your approach to "investment" because it simply rarely works that way in real life.
Good luck in your projects.