I looked at it like this when we went... but this is your pricing for your date
$192 per adult for 11 hours, no food, for 1 day p2p ticket (forgot to check kids price)
$185 per person for 7.5 hours including food, 4.5 hours should be low crowds.
One thing I like about your date is both parks close at 8pm. I think that would help split the event crowd. When we went islands closed at 7 and studios at 9. It really seemed to put most people on the same path starting in islands since it closed earlier. We did have until 130am but they have to close certain rides by midnight... gringotts, RRR, hulk, fast and furious, and transformers closed. Mummy closed for an hour (10 to 11). Also food started 1 hr after park close and food from QS places ended at midnight.
For our experience...
Pros
Some rides were walk ons
Free food
Less time in heat if it's hot out
Cons
Crowd moved together a lot
Rides not being run as efficiently during the day made wait times longer on some
Food places were mobbed/slow... I think part was the parks closing at different times, so islands got swamped at 8 and studios at 10. We ate at a QS place last month on a normal day that we had eaten at during our event and the line was just as long but it took maybe a quarter of a time to get through on the regular day, the event lines were sooo slow.
We had a planning mistake which meant we didnt get to use our dining card, which subtracted some from the value for me but that was on us.
We tried to use our dining card for a drink from a cart before islands closed but they wouldnt let us get in the line 10min before closing
that was frustrating because there were 2 people in line, 10 to 15min out and all we wanted were bottled drinks but we couldn't get in line...
Take with a grain of salt as weve almost always had EP when weve gone... this led to DH saying he would rather just pay for EP or a hotel with it. That's not a straight comparison obviously bc that's on top of ticket prices. I think it could be good value especially with the parks closing at the same time and earlier. I'd maybe go again. And things may have changed since we went back in April, since they will have done several more of them for OI before the UCT one.