I just got back too. I went to all evening EMH's at each park. I found different experiences each time. Like, MGM's was Sunday Jan 2. The fast passes were all gone for till regular closing... at 7pm, they opened them up for wrist bands only, kept them open until they were gone (10:00 return time.) This took less than an hour. So as iy worked, we got one pass, but couldn't get another because by the time we could get one, they were gone

. That stunk! 40-50 min waits. BUT it was still NY weekend. Now for AK, we didn't go and opted another park. MK was Wed. WOW it was great ! No crowds, walked on rides, no fastpass needed !!! BUT that was a slower week too. Then, Epcot Thur, no problem ... walked on rides and got lots of fastpasses for test track, none needed for MS.
SO I think it matters on the crowds at the time.
One Wed Dec 29th I was there 5pm-12 in MK it was crazy !!!!!!!!!!!!!!! Lines were 90 and 100 minutes!!!!!!!!! NUTS !!!!!
Christmas decor and music till about Jan 5th at resorts and parks.
Crowd died down on Jan 2 for the holiday crowd.
I think depending on the regular crowd of that time, it says a lot for if EMH will work or not for that period.
I thought people were getting on rides with no wristband at Epcot, but they were open till 9pm so I was wrong, the other parks closed at 7pm, but not Epcot. I saw them checking wrist bands at all times at all parks.
We walked on Test Track over and over .... it was awesome!!!!

PG