We have had a fairly open design process on team 1726 over the past few years and I have nothing but good things to say about it. The critique you get from other teams in the FIRST community far outweighs any competitive advantages you may have. It's also a great feeling to hear that your public disclosure has inspired or altered the design process of other teams.
Remember, there are over a thousand other FIRST teams with a bunch of super smart students and mentors - odds are you aren't the only team to think of a particular approach. Nothing to lose by showing your progress.