This is a great write up and should be necessary read for every novice (and not so novice) programmer.

That said, I would compose list "What makes code hard to understand?" differently:

  1) improper naming of functions / variables (if you can't name it properly, you can't develop it)
  2) excessive documentation where not needed (document only non-obvious stuff)
  3) *complex* one-liners (because simple one-liners actually help readability)
  4) and 5) can stay. :)

The main point is valid though. I would phrase it like this: optimize for correctness first, readability close second, and don't optimize for performance until you can identify the significant gain (always by measuring it!).