Just got back from my trip so I have an update on this.

1. Came into Terminal 1 on Eva at 9 PM. AA flight scheduled to leave 8 AM next day from Terminal 8.
2. I tried to stay in Terminal 1 to go to a lounge, but there was no way to not have to go through security again after customs. I did try to enter Terminal 1 again, but the minders at the T1 TSA entrance wouldn't let me in.
3. Went to T4. No Clear or TSA Precheck open at 10 PM. Pure chaos in the terminal with people and TSA yelling at people to move here and there, etc. Quite the culture shock after a month in Taiwan. People seemed stressed. TSA agent asked for my passport, explained I was flying out of T8, but entering T4 for the lounge. She said there was no 24 hour lounge and wanted the passport. Provided passport, asked for flight number. She said come back after midnight. Waited in the chapel till 11 till that was closed. Waited at seats just outside TSA till must before midnight. I did finish my book though!
4. Went back just before midnight. no TSA line. TSA agent didn't even look at boarding pass, boarding pass scanned no issue and looked at driver's license, not Passport. No problem entering. T4 TSA wants luggage to be in containers for screening. There were no containers and 4 TSA staff stood around for 5 minutes as we all waited. Eventually someone brought containers and I went through.
5. I had booked the Prima Class reservation for 1 AM for $9 to guarantee a spot. Went to prima class lounge, provided that reservation QR, priority pass, staff person scanned ticket and didn't look at departure time. Note that Stephen from FM was recently rejected at this same lounge since the flight was more than 3 hours away. However, the actual PP rule is maximum 3 hours. Lounge was fine for what I needed it. I did a couple hours of work and then took a 1 hour nap. No bathroom in the lounge, basic food, water, coffee is provided.
6. Walked around T4 for 1 hour. They have a couple cool exhibits.
7. Went to Centurion Lounge for 5 AM breakfast. Note that hot items don't start till 6 AM.
8. Left Centurion lounge at 615 AM.
9. Took airtran to T8. AA first class minders asked if I was in main cabin. I guess I looked like a peon. Checked in at AA first class, went to the back of the TSA precheck line. More TSA staff yelling at people. T8 says do NOT put luggage in containers. Go figure.
Arrived in my office in DC at 10 AM.

TLDR. No late flights from JFK to DCA and no late Amtrak from NYC to WAS means either sorting a bus, doing an overnight in the hotel, or something like I just experienced at the airport.

It wasn't great. TSA staff are YMMV, some are clearly rude and disrespectful and trying to do the bare minimum. Prima Class lounge was fine for what it was. I thought the centurion lounge was good for breakfast. AA first class check in was great and no wait at all.

Would I do it again instead of blowing 40K Marriott points, not sure.