Things wear as they get old, and eventually go from "good enough" to "crappy". Its up to the owner to judge whether it matters enough to put time/money into it, and the market value of the item if resale $ is factored as part of the owner's judgment criteria.

Its no different than home ownership. The old kitchen might be functional, but the remodel adds to the market value and makes it more saleable. Not only that, it improves owner satisfaction. Will you get all your money back? Maybe not, but you can justify it either way, depending on your situation.

The use of the boat is also a major factor. I use mine for daysailing, overnighters, and vacation cruising. If it was used for full-time cruising the wear and maintenance levels would have to be different.