MouseFest only brings in about 1000-2000 people, which is a drop in the bucket at any WDW park. But you will see an awful lot of MouseFest buttons at specific functions like the Osbourne Lights meet (which I think is Friday 12/8 this year) and the MVMCP meet (which is Thursday 12/7 this year).
If you're in WDW during MouseFest please consider attending a meet or two. Almost all of them are free and don't require pre-registration, and they are a huge amount of fun for everybody.