It's tough for me to think in terms of a one day ticket, but I want to start there.
If I had to buy a one day, one park ticket, I think it would most likely be for the Magic Kingdom and I think it edge out the studios at UOR because there are more days at MK where the park hours are longer then they would for a day at USO. I will say though that I have not been to the Magic Kingdom in some time (post LMA, pre-mine train) and I have no idea what FP+ has done to the standby lines while at UNI, I know they have a lot of rides with great capacity, so I know I can get a lot done if ride count is important for that one day.
Now, as a FL resident, that lives far enough from Orlando that I tend to stay overnight when I drive to Orlando. Our version of a 'stay-cation' is to run to Orlando for a weekend maybe around once a quarter. So I like to have an AP for one of the Orlando resorts.
Not sure how longs it's been, but the last time we had Disney AP's we had renewed just before one of their price increases where they started charging adult prices for kids on the FL res. AP's. Somehow all the stars aligned that year and we planned a UNI vacation, on faith, I bought AP's for the family for the trip (in all fairness, UNI does not have a child's priced AP either but the price increase it was going to add for WDW was way too much to stomach).
Now I agree that the one day price is a way the make added days sound cheaper. I assume when we decide to go to WDW again, I will be better off buying some package deal from them. For a day in the MK, we will probably go to a not so scary party as they tend to be less $ than a one day ticket and the queues for the rides tend to be light as most folks are there for the Entertainment. So i just see us going to one of the parties before will would spend multiple nights at WDW. Now, in years past, this option has been hard to stomach because of the cost of one party at the MK compared to the AP HHN ticket where we go early in the event, the ticket has been good for two weeks (I think, might be more), but we have fit in two to four nights over the past few years, so UNI has gotten my funds (this year w/ Cabana as got my hotel nights)) so we haven't' even done a not so scary since our passes expired.
I imagine for Disney, we could have dropped from the pass w/o block out dates to save some funds and I'm not sure we would want to go to the parks during some of those black outs dates...but UNI has shown my family a great time for our visits and we are happy just visiting them currently. The first year we had APs, I bought a preferred for myself, the power pass for my wife and daughter. This gave me the discounts and the self parking and we just restricted our trips to be around UNI's block out dates.
When our renewal came up, the renewal rate looked like such a bargain that I upped the family to preferred. I just renewed for us. After tax, the FLRes renewal was 170.39 each...same as last year...so it just feels these days, UNI and Disney have gone in different directions when it comes to AP's and there bennifits.
I know I have spoken with folks on 'holiday' on some of my visits. The ones I have spoken with seem to be using the Orlando Flex ticket for visits to UOR, Sea-World, and BGT and I imagine the high cost of a one day ticket (at any of those parks) helps make bundles such as the flex tickets look like great deals as well.