I think its a matter of dirty vs soiled. I would probably judge someone if there child was really grimey and smelly.
I have spare clothes in the car in case of emergency. However if its just a bit of food down the front, i'd leave it.
DD goes through at least 3 outfits a day, and DS will change himself if he gets too dirty, I am not going to change them for every little bit of grime or i'd be living in the laundry!
But they are dressed in clean clothes every morning and clean pjs every night