I was a yacht broker for the better part of the year, selling new and used
sailboats in Annapolis.

When I/we (this was taught to me by my fellow brokers) evaluated several
like used boats but with differing equipment, we would usually add the price
of the new bare equipment to the boat to normalizse the prices. We did this
more in evaluating prior sales prices than comparing current listings. New,
bare is roughly half of professionally installed equipment.

I sold one 25 year old boat that during a seatrial had obviously blown out
sails. The seller agreed to cut the sale price by half of the cost of new
sails. In this case you would only recoup half of your investment. FWIW a
used boat is presumed to be functional, ie all of its stuff works. If that
is not the case then there is often a price reduction to be negotiated after
survey/seatrial.

So, if you can do it yourself you can break even (sometimes), otherwise
forget it. As someone else noted, most buyers prefer to make their own
decisions about upgrades.

David