ok.
on what i have read,you are missing one key element to your top 20 and the fact that the mayans calender isnt the end of the world but there given date for the return of what was the ruling beings.
the mayans were slaves(as was the rest of the world) to whoever it was that ruled all those years ago and some may have learnt about the stars from the beings that travelled them.
as a so called educated race we certainly do seem to miss the simplicity of actually understanding what happened all those years ago.
their are too many logical answers to rule out a far superior race than our own.we picked up(and lost)most of what was taught in those early years and anyone can write a book and leave it for someone to find at a later date,the world is full of books with stories,some are believed some arent.
anyway the logic is simple a far superior race to us is set to reappear in 2012 and take from us what it wants and that is what the mayans calender is all about.so please put this at the top of your theory list as all the others are only probables.
steve