Minnie's on average has far more characters than the other character breakfasts (almost double sometimes), and is one of the "cheaper" meals. You can usually expect a selection from Winnie the Pooh, Eeyore, Tigger, Fairy Godmother (rare character breakfast "face" character), Pinnochio, Max (goofy's son), Captain Hook (rare villain), Minnie, Chip and Dale, Rafiki, Pluto and Peter Pan (edited in the last three due to further input). I've heard of Alice and maybe Mad Hatter being there as well but haven't never personally seen her.
So yes, I think it's worth it! I personally prefer sitting inside, as the architecture is beautiful, but the outside is also very cool as you get to people watch!
As for the person who asked about
Goofy's, They have a larger buffet with more selections, but less characters, however they are "big-named" characters. Minnie, Chips, Dale, Goofy, and Pluto. This is one of the most expensive character meals, but my oldest kids loves it most (prob. because of the giant dessert assortment!

)
You guys shouldn't forget
Mickey's Surf's Up at Paradise Pier! This one is my 5 year old's favorite. You get to meet Mickey (only char. breakfast to do so) and wandering around is Goofy, Minnie, Daisy (rare!), and STITCH! Stitch is a blast and makes the whole thing worth it. The food assortment is less than Goofy's, but has things the other breakfasts don't, like flatbreads, and fresh juice/smoothies, whipped cream for pancakes/waffles, and some kind of mexican breakfast dish I can't remember the name of. It's also not as expensive as Goofy's, which is nice.
No matter what you choose, you'll have blast! Have fun!