I danced for 20 years. I started at 3 and stopped 2 years after I graduated college. I knew I didn't want to go professional so I didn't pursue it. But, I still love to dance.
I don't understand the criticism of Julia dancing ability. Sara does both ballet and jazz/modern dance. Just because she knows two different styles of dance doesn't mean she knows hip hop, she's not supposed to be good. She's from the suburbs, not exactly a style you would see training at a dance studio. Sara isn't supposed to know hip hop when she's mostly a classically trained dancer. Think Miss Abby at a competition trying to do a hip hop dance routine and the girls didn't place. It was laughable because it's not her style of dance nor her style of choreography.
So actress first, dancer second because most movies about dance use real dancers to fill in for the actress anyway. Jennifer Beals wasn't a dancer, she was an actress, the director and producers used three professional dancers, one being a guy.