I'll just list off what we did, and want to do. We bought our boat (1998 Hunter 410 in March 2016), and have been customizing it to our needs ever since.
Completed zero regrets...
Whale Grey Water IC replacing shower sumps.
Additional whale gulper pump with hose to be able to vacuum the bilge dry
Ocean Marine Davits
New sails/stackpack, and Tides Track
Espar Hydronic Heat
LED lights inside
Replaced factory raw water strainers (plastic) with heavy duty bronze.
Changed from 2x 4D batteries to 6 T125 6 Volts for a 750 amp/hr bank and a Victron monitor
Rocna 25 kg, and a mantus bridle with chain hook.
New speakers (wetsounds), and Sony Marine Deck with a Class D built in amp (400 watts)
To go...
New Instruments
Replace both heads with fresh water electric
Add cabin fans
Add flexible solar
Exterior lights to LED
Might do...(long term low priority)
Engine blower/extractor
Code Zero or A-sail on a top down furler
Anchor sail
Fuel polisher system (not likely)
Balmar high amp alternator/regulator (once we see how solar manages our needs)
Fridge/freezer works well, (OEM), but it's likely at some point it will be renewed.
Completed but would have done differently...
We had a nice canvas dodger/bimini made. I wish I had instead made a solid bimini that was capable of being walked on. The boom is really high on this boat. Being able to climb up there to work would have made life easier a few times when removing the mainsail, getting the sail in its bag, etc. Also I should have better factored in solar when doing the dodger/bimini design. I'd still keep a Sunbrella dodger, and joiner to the bimini.
If money was no object...(super cool things that are too much money for the way we use our boat)
Replace the aft holding tank to a Purisan System from Raritan.
Replace the Max-Prop with a Brunton Auto Prop.
Gone with carbon foam batteries rather than FLA.
Used Hurricane Heat rather than Espar (Espar is very good, Hurricane is simply the best but was too much $$)
Build a purpose built anchor roller for a 30 Kg Rocna, upgrade the windlass with a chain counter
Extend the stainless pushpit all the way forward to the boarding gate
Rarely have I wanted a bow-thruster, but one or two days a season it would have been nice.
No Interest in...
Electric Power, being able to motor to weather if a time critical issue arouse, (rescue at sea, illness, torn sails, rigging failure), and electrics minuscule range makes it less than appealing right now. For a day sailor or a weekender though I can totally understand the appeal.
Wind generator, noisy
Drag behind water generator
Changing the interior layout, we love it as is. The only place I find the boat lacking is deck storage. The lazarettes are smallish and the lockers on the swim platform aren't in a safe position to access when under sail. However I wouldn't cut up and replan the interior to gain space back.
A TV mounted on any bulkheads. An iPad or laptop is all we need for screen sized entertainment.