Yes - wear them in the parks (really where else can you?)
I don't wear the "hat" ones because I have a big head and a lot of hair (which is often in a pony tail or bun when at WDW) and find they don't fit quite right but I have a number of the headband kind. There are so many different kinds, I have several different pairs and try to get something new each trip. I have black minnie ears, gold ears, silver ears, stitch ears, tigger ears, every colour of bobble mickey heads on the head bands and I'm thinking a few others that I can't recall right now.
Choose the ones you like the best and wear them with pride.