We just got home from WDW last night. We used fast passes for the princesses on Tuesday but not for Mickey. I grabbed passes around 1pm when we were waiting for our lunch ADRs at the Plaza. We used the fast passes much later when we came back to the park to see the fireworks after taking a break at our resort. At that point the standby line was 40 minutes for princesses but we were thru in less than 10 with our FP. The standby line was 15 minutes for Mickey/Minnie, but we skipped them that day. The fastpasses are connected to the others in the park (so they prohibit you from getting one for a ride during the same timeframe). The CMs did not have a problem with us using ours past its time, but maybe if the park had been crowded, they would have cared.
Friday, as we were headed out of the park for the last time before heading home, at 2:30 pm, the wait for Mickey was only 5 minutes so we stopped to see him and Minnie as our very last thing before heading to the airport. We had already seen them at character breakfasts and at other points during vacation, but we were all thrilled to get to hug them goodbye and thank them for helping us have a magical vacation. The park was not very crowded and many people were lining up for the parade at that point (we'd already seen on a previous day and were headed out before it started). It was the
perfect way to end our week at Disney as their meet and greet is literally just a few feet from the exit to the park.
I would say that the princesses are worth fastpasses. Depending on crowd levels, Mickey and Minnie may not be. As Mickey/Minnie don't talk, the interaction with them is relatively short. However, there are 3 princesses in the greeting room. They were super sweet and took their time talking with all the people who were there to see them. Consequently, the princess line is much slower. They have it very well organized, and (potential Magic spoiler alert) they apparently have at least 2 identical rooms for Mickey & princesses going at the same time. They take you from the main holding area into a hallway with several doors. Then they open a door, let you and a few other people in to where the characters are and close the door behind you. So unless you are paying attention (or have someone point it out to you), you might not realize it.
3 princesses in one room. Each one has a handler, a photopass photographer, a bench for seated photos and a large feather pen for signing autographs. We saw Cinderella, Belle, and Aurora.
Standby wait time for Mickey/Minnie on Friday @ 2:30:
What better person to hug you goodbye on your way out of the park for the last time?