If you've gone many times, it's tough to say what you haven't done before. Initial thoughts:
- explore all of the resorts. They all have unique sites, activities, dining, drink options. Many have night time entertainment or special views of the parks for their entertainment. Disney Springs also has entertainment at night. Many areas also decorate differently for the holidays. Many are manageable in an hour or two. Some of the DVCs - OKW, SS and a couple of the moderates - POR, CBR, CSR are fairly large.
- you mentioned boats in Seven Seas Lagoon. Did you also go over to Bay Lake? You can see Discovery Island, some remains of River Country (probably less now than before though), and FW and WL, You can also rent boats at the Yacht Club and go around Boardwalks, Swan/Dolphin, DHS
- While we're on transportation - take all 3 of the Skyliner routes, and the resort and TTC-Epcot monorail routes. I'm guessing you've done most of these though.
- Other boat rides - Springs to OKW, SS, and to POR and POFQ, also Epcot, Boardwalk Resorts, Hollywood Studios
- the two miniature golf courses
- AK - all of the animals, nature trails, Rafiki's - lots of people skip these but there's a lot to see
- MK - unique views - you can see the fireworks from behind the castle. Not as immersive but neat since it tends to be quite empty and you can sit on a bench and enjoy them differently. Same as from Poly's beach. Some of the buildings around Main Street like the fire hall are often skipped by people.
- Epcot - the grounds and shops around the countries - non-shoppers may skip the shops but they're worth a browse since they try to have unique things to each country. The grounds have hidden gems like the bonsai trees in Japan and the gardens in general. Not sure if they're letting people into it anymore but in the back shop of the UK (Toy Soldier) is a room made up like Christopher Robin's room. It's not advertised but if you find yourself the only one in the shop during the day and ask nicely, you might be granted a viewing. This one is rather obvious but if you've never been in the Seas building, there is a huge aquarium on multiple levels worth a look. They also feed and talk about the manatees on the top level. Probably not open now, but there are packages that would let you even dive in the tank. If you're lucky you might see some of the workers in there.
- DHS - in Galaxy's Edge, there are things you can interact with on the Play Disney Parks app. You can translate the Aurebesh signs, scan containers for cargo, and even take on assignments.
