As a coach/mentor, not sure how meaningful my answer is to the poll, but here's my opinions on kits based on years of coaching .
For a new team with no stash of materials or experience, kits, while expensive, can be a very good way to get started and fairly quickly have a plane that FLIES. It can save a lot of time trying to gather the materials you need to build from scratch. And that's critical, if you are not flying, you aren't learning. And if you aren't flying, you are most likely getting discouraged and thinking you can't do it. All very bad for new teams.
Frankly, at this point when I coach a team (as opposed to a clinic) I spend the first session having the students build a simple plane like a Delta or Denny Dart FAST and flying it THAT DAY. I don't even attempt to build anything that's WS competitive. I want students to see they CAN build and fly a plane. That gets students interested enough to spend the 4-5 evenings to then build a good WS plane and see how much better a plane can fly.
For a team with a stash of materials and some building experience, but perhaps not WS, kits are an expensive way to get plans and materials. Better would be to do some research on the web to find plans (there are many old WS plans out there that can be easily modified to any given years rules) of successful planes. Then dig into the stash and start selecting materials to build those wood selection skills.
For an experienced WS flyer, say you flew last year and have some skills, perhaps not the best, kits are a step BACKWARDS! Take the money you'd spend on a kit and buy the raw materials. Learn how to select wood, its not hard, you don't need super wood for WS, we design the rules so you don't. And buy rubber, lots. Spend time building many planes with variations you think will help and FLY LOTS.
And for WS flyers who can build an F1D, your scrap wood is better than most kits and you can design a good plane in your sleep at this point, or know where to pull a good design from the web! Kits, yeah...
That brings up one thing about kits that can be limiting. Most only include enough rubber for a few motors, at most maybe 10. That's no where near enough because it leads teams to be more worried about breaking their last motor instead of maxing out the flying time. I've seen way too many good teams come to contests but fail because the competitors were afraid to wind their last motor and break it! Guess I'm suggesting if you use a get, buy extra rubber!