No, the vast majority of courses only use ATAR for selection.
For those that don't (mostly medicine, scholarships or if you are applying as a talented athlete), they would probably only care if you were presenting athletic prowess as an extra curricular activity/talent of yours that was applicable to the program/scholarship you were applying for in some way.
Even in that situation, I suspect anyone in that position would have better things to talk about than school carnivals.
No. I definitely recommend going to every carnival you get the opportunity to go to though because you will very rarely have the chance again to spend a whole day dressed up, mucking around with your friends and having fun out in the sun once you finish high school. Take every chance to do cool things at high school because let me tell you, you won't look back and remember the days you stayed at home and studied/gamed/whatever by yourself.