Sharing my experience with Express transportation Tuesday, July 4th. This was our one and only day at Disney since this was a Universal trip.
We started the day at AK and took the 11:00 bus to MK (we had debated going to EP before MK -- wish I had now because we were at MK for way too long that day). Everything went smoothly and there were only 9 people on the bus, including us.
After the 4th of July fireworks, we headed back to the Express bus stop to catch the 9:30 bus back to AK. There were about 20 of us this time. Even with the end-of-the-night traffic leaving MK (especially after the very crowded MK fireworks), we were back to AK by 10:00.
Since we didn't have to go through security, etc., we just walked very fast over to EE, rode it twice, watched ROL, and went back to Pandora (after being there that morning) to see it at night.
Even though I spent $76 for one day, I felt like it was worth it for us. Granted, the weather cooperated and I wasn't stuck in a situation where it wasn't operating or dropping us off at the front the park, so luck was on our side that day, but I have no regrets about spending the money just for 2 hops since it allowed us to do everything we wanted to do on our one Disney day.