I am an avid supporter of the F1 Grand Prix, and have always attended yearly!
FYI, It's pronounced "Graun Prie", it was so embarrassing to have to tell a colleague she's pronouncing it wrongly before she went up to stage to talk about it, but... it needed to be done.
So, the F1 Grand Prix is like, an "ATAS" sports event, so you don't really want to be typically Singaporean and underdress too badly (though it will be hot as hell).
The women who attend F1 races are from all over the world, and are definitely more fashion conscious than Singaporeans are.
Just because you NEED to dress comfortable doesn't mean you have to compromise on looking good and being stylish. Be classic, elegant, and have fun at the event!