This was my first year as an assitant coach for a Lego First team (elementary age) in competition. (I previously did a Jr FIRST team but we did not compete). I don't think I will participate again, here is my feedback from this season.

The positive.
Programming: The kids learn to solve problems and gain basic programming skills. My son enjoyed this very much.
Teamwork: It was very rewarding watching two kids tackle a problem and solve it together, and learn to listen to others' ideas.
Service: I like the idea that we tie the challenge to a real-world problem to get the kids thinking about something other than themselves.
Legos: Next to programming, building the kits was my son's favorite part.

The negative.
Price: Each kid paid $100 to join the team. I think that's a very high joining bar for this activity. I think I'd rather put that aside to buy my son his own robotics kit.
Limited opportunity to program: We only had one laptop to do programming. This meant that in a team of 7 only two kids (at most) could do the programming portion at a time. We divided the kids up into three groups in rotation, and each spent one-third of the time on either the programming, the project poster or the core values poster. This meant that only 1/3 of the time were kids able to work with the robot, which is the ENTIRE reason to be there.
Core Value and Project posters: I hated, hated, hated this part and so did my son. Nobody cared about the posters, everyone wanted to do programming. This portion was extremely adult-dependent as the instructions for completing the posters was confusing. It was just like the stuff they do in school, and nobody wants to join an after school program that just gives you more schoolwork. As a coach I really had to force them to do it over much whining and complaining. I have previously done other coaching activities, from Scouts to Soccer, and we sure didn't spend 2/3 of a soccer practice talking about it or making posters about it.
Unfair competition: Our team was made up of kids from 4th and 5th grade. At the competition, we had to compete with middle school kids. Due to the wide gap in skill and maturity, of course the middle school teams rolled over the elementary teams. I don't know why they didn't divide the competition up into age or grade groups. No one would put a 4th grade soccer team against an 8th grade soccer team. Intellectual competition shouldn't be any different.
Time commitment: Of course this will vary due to how different coaches work. Mine wanted to have two THREE HOUR practices per week. And I might mention that if you haven't tried before, it's VERY hard to focus elementary school kids for an hour at a time, much less three. And as a coach, this was far more time than I was really able to commit given my personal schedule.

So I encourage your comments on my feedback. What did we get wrong? What should we have done differently as coaches to get more out of this activity? Is FIRST worth another try? At this point if I want my son to learn robotics and programming I think the time and money would be better spent with him one-on-one.