[blueyoshi256]

I think I have something meaningful to add for once.
Our team is not too worried about people who aren't always there. We have about 30+ students on the team, only about 15 of whom are hardcore, and show up all of the time. That's okay to us.
How we cope is through management. As captain last year, pretty much my sole job was making sure everybody else was able to work productively. Sometimes, it was as simple as finding them a tape measure. Mostly, it was pointing them in the right general direction, and occasionally, I had to walk some of them through everything.
It is not an ideal system. I think we have many students that don't believe they can do the task they are given, and are so afraid of failing that they forget to start. We have tried having mock build seasons in the fall, and our lesson system is posted on here. These have helped a bit, but the problem still remains.
This year, we are trying something new: FTC. We are hoping that less intimidating robots and a longer build season, plus veteran team members helping to teach rookies, will be enough to raise our average skill level.
It may not work. That's a scary thought, but it is okay. What is important is that we are trying something. Maybe the solution is not FTC, but Lego League in the junior high. Maybe we should go back to our lesson system. If we keep trying, we can figure it out.

TL;DR: Not all students need to be hardcore. Having some who manage the non-hardcore students helps a ton. Try stuff (like FTC) until something works for your team.