@JTT,
Not to resurrect a thread casually, but after reading through all of that I couldn't resist.
After reading through, I was left feeling like you have all made an assumption which I think needs to be challenged. You have assumed that the written language needs to be changed to match the spoken language rather than the other way around. I think that the written language is the more important one, and speech is simply one way of expressing it. Although my day to day job relies on creating things that people have specified in writing, so I may be slightly biased, as I spend most of my time simply trying to get them to clarify exactly what they mean, and record it.
Maybe 30, or even 20, years ago the spoken language was much more important, but in this day and age, the written language is at least as important as the spoken, if not more so. However, as the written language doesn't have the immediacy of the spoken, it needs the complexity to be able to convey meaning correctly.
If I write something, I want to know that the person reading it, understands it in exactly the same way that I intended. The whole purpose of having standardised spelling and grammar, is to enable just that. A simplified, or fully phonetic, language would remove a lot of the tools that allow me to do that, as it is weighted much more towards the spoken word than the written.
A lot of the complexity, and quirks, provide some much needed disambiguation. A relatively simple example of bare and bear, these two different words happen to sound the same, so a phonetic language would have them spelled the same way as well. However, that would make a reader unable to distinguish them. You may be able to infer the meaning from the context, but you would never be sure, one hundred percent, that the person reading it would choose the correct version. Spelling them differently clarifies to the reader which of the two words was intended with no ambiguity whatsoever. If getting it wrong meant the difference between entering a room containing either a naked person, or a wild animal, you would want to be sure they got it right first time!
Spoken English, does not need this as much. Along with being able to gauge an immediate reaction, there are many ways of conveying additional meaning such as tone, emphasis, pauses, even facial expressions or hand gestures can be used for clarity. All of these things need to be conveyed, somehow, in the written form of the language. This makes it, necessarily, more complex than the spoken.
An example was given earlier about the possibility of a great writer who has never written due to not being certain of the language, however, a great writer may never have their work spoken aloud. It's written to be read, not necessarily spoken. Also if each reader interpreted the text in a different way to that which the original author intended, as the language was too simple to express their meanings clearly, the chances of them becoming a great author would be slim.