I love Goofy's - that is a must-do for almost every
Disneyland trip I take (since 1992!) - but I fall on the pro-breakfast side. I was not crazy about the dinner when I had it but, admittedly, the dinner I had was years ago and things could have changed since then. Plus, dinner is more expensive than the breakfast. But some folks just prefer a big dinner over a big breakfast.
Either way, the buffet is huge so you will have tons of options at either meal, but there seem to be fewer good reviews of the dinner than the breakfast.
Goofy's opens at 7:00 a.m., so you won't miss any park time if you do breakfast! And you have a full 90 minutes to eat and wait for characters.