I'm doing the same thing right now, trading in the 2017 MX 100D for a 2024 MYP.
The FSD + Free Supercharging + Cybertruck extra $1000 off + Tax Credit right off the top at purchase time + $1000 off in february made the deal too sweet. I already also had a 2023 Y, so now both me and my wife will have Ys
I have lived with both the X and the Y and here is my take:
Things we'll miss from the 2017 Model X
A) Air Suspension, Its very smooth even over a newer Y with comfort suspension.
B) Wow Factor, still nothing much like it on the road and still turns heads 6 years later (good and bad)
C) Automatic Opening Doors
D) Panoramic windshield (It's so unique and fun to look through, especially when visiting national parks or scenic areas.)
Things we won't miss from the 2017 Model X
A) The falcon wing doors are incredibly nice for ingress, egress especially with small children, car seats, old people , but our children are older now and opening and closing the falcon wing doors takes several seconds longer at carpool than it does in the Y. In the Y the kids just jump out and shut the door and we go, the X isn't bad at all, but the Y is just simpler and quicker to go.
B) The 2017 Model X cup holders are awkwardly positioned also I feel like all the center console features in this car are just a bit strange and awkward to use, I won't be missing this.
C) When your air suspension module on each wheel eventually starts leaking, its $1000 a pop to fix, (we've replaced 2 already) I imagine at some point when the fancy doors fail it could be a disastrous repair bill, moving to the Y we will be in warranty again and future repairs will most likely be cheaper than they would be on the X.
D) Even though we upgraded the media center console, its still much slower compared to the Ryzen powered ones in the Y.
E) The falcon wing door pads rub the paint, so I have to replace a strip of PPF on the door frame every year so this doesn't happen. I won't have to do this on the Y.
Things we are looking forward to with the New Performance Y
A) FSD works better on the newer cameras and hardware, being able to transfer it is SO nice.
B) Center console and cabin environment is clean and well laid out.
C) We'll be under warranty
D) We're able to almost trade the 2017 X straight across selling it 3rd party (at least it seems so based on current prices. They've dropped a lot and I still have to find a buyer, but can't sell until new one is delivered and FSD is transferred anyways.)
E) The Y is zippier and more fun to drive, easier to navigate in parking lots, my wife and I both enjoy a sportier drive.
Regarding replacing with a new X vs. new Y
A) A new model X in my opinion isn't worth the 35-40K extra over the Y unless you need to comfortably seat 6 or 7 people. We had a 7 seater X and they spent the entire life of the vehicle folded down except maybe 5-6 times we used them.
B) The model X is more spacious, we were able to fit all our camping gear plus a small inflatable boat which I don't think we can do in the Y without a special rack or cargo storage hitch, so X wins there, but still.. for the 1-2 times a year, its probably not worth the expense. It's just really hard to justify an X when the Y exists. While the Y is not as big as the X, it is still has a LOT of cargo space.