I agree with you in principle, but I doubt Y!A will listen to us -- we are but a small segment of the Y!A universe.
I like Y!A for three reasons: First, to teach others, Second, to challenge myself and to learn, and Third for entertainment.
I love the math and sciences. I have an engineering degree from a top US university. But I don't practice engineering anymore. And until I rediscovered my passion a few years ago, I had been many years without doing more than trying to balance my checkbook
I mostly answer Physics questions. My skill level is currently that of a lower division, quasi-honors student at a good university. My math skills are a little more rusty, but I can do trig, geometry and calculus -- but there are a number of holes where I have simply forgotten how to do something.
Beyond answering to help people (which I do), I also look for challenging question to learn from. I find challenging question two ways:
(1) I ocassionally search the Physics' section for questions with "AP" "College" or "University" in the title,
(2) For math and some physics, I have a large group of contacts that occasionally ask interesting question, or star interesting questions. My contacts include AB, MD, RD and the Great Locust (Sorry, without having the names in front of me, I will misspell one or more, so I am using the initials for short). I have discovered for the math section, at least, Y!A has a serious group of top contributors that have formed a high-level applied math and mathematical puzzle section, which you have recently stumbled upon. So, if you see questions in math from a "Top Contributor" or a question that has gathered several stars from Top Contributors, you can assume that it is a challenge question which the questioner already knows the answer.
I am also a bit of a xenophile and I enjoy the fact that my contacts are flung across the globe. I have contacts in Eastern and Western Europe, Canada, India, the UAE, Singapore, China, Japan, Brazil, Australia, and a little village of Native Alaskans (eskimos -- sort of).
So, although there is no Y!A for applied math and physics, I have developed a good work around. And I am better off for having developed a set of diverse contacts.
[I get entertainment from Y!A both by solving problems, but also by an ocassional foray into some of the lighter weight sections of Y!A like politics, polls&surveys and religion]