I am not concerned about the men at the track seeing me change, however, I am very sensitive about protecting the kids at the track from seeing too much or from offending the parents who bring their kids to the track. In Michigan, if you are ticketed for exposure, you have to register as a sex offender--and I'm not interested in being a member in that group so I do my best to be modest.
To protect young eyes I wear a sportsbra and one of my boyfriend's t-shirts to the track. I find that the long shirt allows me to stay pretty much covered while I put on my knee guards and pants. My sports bra looks far more conservative than most bathing suit tops, so I don't worry about exposing myself once my pants are zipped up. I have a couple of halter sports bras, which are really great because I feel comfortable taking my jersey off anywhere and at any time--because they look just like a shirt. When I am done riding and kidlets are present, I put the long t-shirt back on over the sportsbra and ride home a little soggy..but happy knowing I didn't offend any little ones.