I would not waste a days admission just to go to E-ride nights. E-rides are awesome, for example, we did Splash Mountain 7 times in a row, and never got out of the log! But, as stated, you have to have spent the day in a park to go to E-ride, so it is not worth it to waste a days admission just to do E-rides.
We go in August, and E-ride nights are usually offered 2-3 times per week. I would try to find out what other night they are available when you will be there. IF there is no other night, I would skip it because if you get to the MK at 4:00 p.m. you are not maxing our your buck for the day.
You have to stay in a park resort and buy a minimum 4 day hopper pass to purchase E-rides. Last summer they were about 12 dollars and well worth the extra 3 hours in the park. Rides open are Splash Mountain, Thunder Mountain, Country Bear Jamobore, Haunted Mansion, Space Mountain, Orbitor, Buzz Lightyear, Extra Terrestrial, and the rocket ships. THere might be a small wait, but usually not more than 5 minutes. Depends on the weather too. One time we went in the rain and there was no one there. IT was great!
I always buy my E-ride ticket when I check in at the hotel, so I know that we have them. Then, usually we go to Animal Kingdom on the day we do e-rides. Sleep in and get to AK about 10:30 a.m. and we can finish Animal Kingdom by 3-4:00 and go back to the hotel to rest up. THen, we get to MK about 8:30 to get past the fireworks crowd, get our wrist bands as soon as we enter the park and then head over to either splash or spash mountain, watch some of the fire works, and then we are in a great postion to start e-rides. E-rides start at 10:00 p.m. in AUgust and go to 1:00 a.m.
Sometimes, we do e-rides more than one time in a week. THey are so worth it! Anyone can stay in the park during E-rides, but only those with wrist bands can ride.