You make a great point here, but I'll tell you the problem with it mainly with youngsters.
More than likely they won't develop any sort of real creative process with this just starting off. It's highly uncommon to find someone who is just creative naturally and just comes up with things on the spot with little revision needed.
The way they are starting off by learning some sleights and then just moving cards around with sleights used in different ways isn't the right way to start off. Let it come to you, this is the best starting point because it opens up the creative process for you now.
Once you learn what a great idea feels like, looks like, and how it came about you then you can truly "try" to come up with effects. This doesn't mean you show every effect that you come up with now, you don't want to be Sankey in this and release so much crap that people just won't trust your material.
Build off of what you know now and believe good things will come, it may be in a hurry or you may stall out and take awhile before something comes, but something will come.
Two side notes here, one about the quote, the people that come up with tons of crappy ideas are usually paid for this type of work no? Quite often it isn't crap, it's just that it needs elaboration which isn't what companies advertising want. They want catchy slogans and phrases and things that can hook the listener quickly.
The second is about Sankey, I dislike much of his material because it's just variations on so many old things. Some of the old things are not very good in the first place or his variations don't improve on an already great effect.
I recently received 22 blows to the Head and so much of the actual material was just a magician showing how little he really understands about mentalism. I am not calling myself an expert on the subject, however I do understand a thing or two and listening to him just annoys me.
He could be so amazing with his creations, but he doesn't sit back and rework his material and fully appreciate it. He sells w/e people will buy, and in this case just a hit or miss buy. He has some great thoughts, yet still comes out with some material that is pretty much just crap from the beginning or like you said just gems he didn't polish because he was working on his latest effect.
I don't know about "just letting it come to you" though. Perhaps this is too ambiguous. What would be bad about figuring out a method to an idea? Or what is bad about showing people your ideas, good or bad? What harm is done from learning that way? Is it just the annoyance of reading " I created a new sleight!" and people replying "no you didn't. that's called the double lift"? I do agree you shouldn't market every garbage idea like it's the perfect trick, but I would submit that there is very little harm in learning by trying out new things. Sometimes you learn something, practice it a ton, then show it to a few people, and they are not impressed. You figure out what was wrong and work it out. And if you reinvent the Marlo tilt, then so be it. What harm is done? Why is that a bad way to learn?
And using Google as an example again; when they collaborate on a project for example, they will toss a lot of bad ideas from a lot of people, until they get one that is workable, and yes they still pay all those who gave bad ideas, because tomorrow, they may have a good one.