We love Minnie's Breakfast at the Plaza. If your daughter likes characters, it is a great place to meet them. We always book a late breakfast there at around 10:15 or 10:30 and have never been sorry. We get there at opening and spend some good short line park time before breakfast, and then go take a break and eat a meal and see the characters. At that time, the place is typically not that crowded and we have seen up to 12 characters and never less than 7. We also have gotten so spend quite a bit of time with the characters. Minnie has grabbed DD's hands and taken her dancing more than once during the meal. You never know who you are going to meet. We run into the Fairy Godmother about every time, which DD loves. I will warn you that they recently standardized the character's at Goofys to a specific 5, so I don't know if they might do that to Minnie's soon.
One warning is that Captain Hook is often there, which might be a bit scary for a 2 year old. He will back off if a child is scared of him though. I recall DD hiding under the table when he came up to us our first meal there. He was able to coax her out though and by the end of the meal she was doing the Macarena with him which was quite funny.
Minnie is at the front of the park in the mornings quite a bit. She is not always found at her house in Toontown during the day. I would say that more often than not, she has not been there when we are in Toontown. If she is there, her line is often really long. I'm sure she is always back there at some point in the day, but the question is when.