Philosophically, I've got an old boat that will need 5-10k (easy) of repairs and upgrades over the course of a few years to be what I want her to be. I want a capable bay cruiser/entertainer solid enough to poke out into the Atlantic in 100 mile weather windows.
On the topic of upgrades -- things learned through hard experience (and losing a lot of money.)
1. I am guessing that this is a bit of a starter boat and not very expensive. You will never get even close to the money back from expensive electronics. Engine upgrades on an old cheap boat are a fools game. You might put $15,000 in an engine upgrade. If you recover $1,000 you are doing well. Put the $15,000 into an upgraded boat. Yes, people re-power their boats. But usually these are boats they have owned for a long time, are still worth a bit of money, and they like the boat a lot.
2. Just because something is on the boat you don't have to sell it when you sell the boat. It is a little difficult if you have drilled big holes in the fiberglass to mount things, but even so you can take things off. Dinghy, outboard motor, anchor, and chart plotters (mulit-function displays) are things frequently taken off the boat.
3. Sails - you can pay a little or a lot for a new sail. Unless you are going to seriously race the boat new sails are another thing to pass on. The only exception would be if they are shredding or are "blown out." To test to see if your sails are "blown out" place your mouth over a section of the sail. Blow hard. If the air goes through your sails are "blown out." This means that they are stopping only a percentage of the wind. If you have to purchase sails consider getting used sails. There are several sources, one of the big shops is in Annapolis - not that far from you. You will find them much cheaper and adequate for your needs.
4. Shop the marine consignment shops. This takes a bit of patience as they are filled with crap. But frequently you can find something you need used for a lot less than the new price. Also shop the Internet - Jamestown Distributors, Defender Industries, etc. You will find them less expensive than West Marine over time.
5. Look for parts instead of things. The bracket on my hailing loudspeaker broke. A new loudspeaker was about $50. I searched the Internet with all the numbers on the speaker until I found the manufacturer. New bracket $0.99. Cost of shipping $5.00. Sill a lot cheaper than a new speaker.
6. Don't go exotic. Electric drive? Sailboats are always
short of electricity. Your Atomic 4 was the mainstay of the gas engine world for years. It has been replaced by small marine diesels. There is a reason. They are cheap, efficient, and last forever. An exotic electric drive will turn off 95% of the future buyers of your boat.
7. If I were to put one upgrade at the top of my list given your cruising grounds it would be a transmit/receive AIS. It will make you show up on the displays of all the big ships. Typically it will also alarm in their bridge if they get too close - but they can turn that alarm off.
A little checklist for when you drop the mast: Sailing - Reboot (USA 60493): Things to do while the mast is down
Fair winds and following seas.