Its awesome that you are capturing such detailed ideas now, while it is all fresh in your mind and you have time to plan and act without being in panic mode.
I like your idea of developing your median students in the preseason. And I think incentivizing it can potentially help. 1511 tries to get every single student on the team to lead up an activity like a demo, a fundraiser, or a community service. This gives them some of the leadership skills outside of the "robot", and helps them better understand planning. 1511 also set up incentives... they have
Achievements that each team member can work on in order to earn team funding towards their travel. Now for the caution... I find this generation of students less incentivized by money than even those from 5 years ago. I don't know if its just that parents are more willing to just pay for everything, or entitlement, or what, but be prepared with a backup plan and/or alternate ways to encourage kids to tackle these roles.
The other caution is that kids are often afraid to fail, and I think you have the right idea that they get credit for leading, not for successful projects, but then they may be worried at failing as a leader. Its hard to quantify what "doing a good job" is without some sort of success or metric tied to it. But I think ultimately, if they understand the REASON for doing this activity, you are more likely (though not guaranteed) to get the result you are looking for.
So we often use preseason as a training ground, where student can join or learn whichever subteams they want, but then we get more selective for build season.
Onto the build season... my initial read was the same thing Greg brought up... if you have an elitist core, break them up & force them to be individual leaders. Whether you have drivetrain, collector, and shooter groups, or electrical, programming and mechanical groups... split up your core leaders and let them be a little less reliant on eachother. They can act as an integration team, but ultimately, they will have to bring up the students around them in order to get the job done. One thing we implemented with our build season subteams was to make sure that every team had at least 1 experienced, 1 new, 1 CAD student. If the subteams got bigger, we tried to blend as best we could, but there were always cores, medians & outliers on every subteam.
Your ideas may or may not be ambitious, but keep trying new things and see what sticks. The beauty of this program is that there is no one right solution. Good luck!