Just a quick go... too many points to address, too little time to do it.
First I'm coding a little program to easily produce 2- or 3-column parallel texts for language learning. If anyone's interested just drop me a note.
Now languages... in many countries, language 'grammar' is not taught at all so it can't be learnt as such. In those where it is, most natives quickly forget it just like they forget most of what they're taught at school -- because they don't see any practical value to it. I happened to see how it strengthened my language knowledge and skills from the get-go (my first 'grammar' memories -- I was maybe 5) so I never resented it. Needless to say, a great deal of it was immensely practical when I started learning foreign languages so I consider it essential if only because it's such a big time saver. Same goes for phonetics which I wasn't taught at the time but in retrospective I can tell you it's just as useful as grammar for foreign language learning. Unfortunately it's not evident to most people how useful such things are.
In the same vein, nowadays a lot of foreign language teaching is done by natives (only reason they're hired, apparently) with the thinnest of knowledges, albeit with only a semblance of formal training which unfortunately actually involves none to just very little of the above. I know because I am one such certified teacher, except that I wasn't native. In comparison, extremely little of what I know I've learned during my 'formal' training -- since you can't effectively teach what you don't know inside out, that clearly accounts for the currently 'sucky', poor state of FL teaching.
@ficbot: vocal cords are speech support structures 'only'; granted you can't speak without them, but you don't use them to make most of the differences between sounds -- that you do with your tongue, jaw, lips, etc. so maybe (I don't think so but won't argue here) human speech really gets calcified after a while, but it's not because of the vocal cords, if anything it would be about untrained mouth movements or maybe neural patterns.
For those interested, there's
an awesome forum about language learning called 'how to learn any language' where I've been posting for a couple of years now.