Bryce Harper will be making his pro debut in Rome Georgia tonight. Harper was the #1 pick in the MLB draft last year, but is starting the year playing for Hagerstown instead of Washington. I'm guessing a lot of people who go to games have not heard of Bryce Harper. Drafted players in MLB have a much smaller chance of making or staring in the majors than NFL or NBA players.
Recently my colleague Tom Rhoads and I did a study showing that having a top prospect on your minor league team had only small influence on attendance (at most a few % increase). The paper will come out in this June's Journal of Sports Economics, I'll link it then.