I think GPA is important, but not most important, to the holistic review of colleges. Most look at all that you've done, and also admissions officers often look at your record in the context of your school. (For example, not all schools offer as many AP classes as others) Also, recommendations and interviews are increasingly popular, and these can showcase your abilities outside of class. If you're spending so much time in robotics, maybe your teacher would be a great person to ask for a recommendation!
My school has a "brag sheet" for us to fill out before a counselor writes a rec, and one of the questions is "Is your high school academic record an accurate measure of your ability and potential? If not, what do you consider the best measure of your potential?" I don't know exactly how my counselor will reflect on that (if she does at all), but something like that may be a good thing to put in your applications if there is a spot (i.e. the Common App's personal statement box) And yes, some schools calculate GPA differently, such as the University of Tennessee, who unweights them and recalculates only certain ones (and if you've taken more than what is required, they may only look at your highest in that subject. For example, I've taken 4 art classes total, but UT would only look at my highest unweighted score.)
But yes, I do agree that GPA stacking is a problem. Not only does it sometimes unfairly inflate GPA, it also takes away from other experiences you could have in high school. I am an excellent student in AP and honors academic classes, but I have also taken leadership, theater, photography, speech, wildlife, and leadership. Are those going to make me appear a weaker student because I did not take certain AP's? No - if anything, they will show that I am well-rounded. Plus, I'm not interested in all the AP's my school offers, nor do I want to sacrifice parts of my schedule to take them.
Now, back to robotics. I can say that I would not be in robotics for my 4th year now if I had had to give up some of my classes (on my school's block scheduling, that's a whole semester if I took it once a year!). But I have an idea for you. See if you can create some kind of robotics-related project outside the competition. Maybe you can do research, or solve a problem through designing something. Make this opportunity available for students who have done robotics for at least two years (or one so that it can add to GPA sooner) and make it so that their participation in that can count as honors credit. This could be done in the offseason so that it would not interfere with the REAL March Madness.
(Source of the idea: My school has a STEM Scholars program where about 20 juniors and seniors are in groups researching something. We haven't started our research yet, but upon completion, we will get an extra certificate at graduation, and we can put this on our resumes. All this is out of class, although some get permission to reserve a class period to focus on that instead of taking a class.)
Hope this helps!