....” has anyone ever seen a cogent and insightful strategic explanation for why Russia decided that, what the hell, and invaded and annexed the Crimean peninsula?”......
Easy...payback... and because he could.
Crimea has a different history and different ethicity than the Ukraine. It was never part of the Ukraine until Krushchev redefined some boundaries in the 1960s (I think).
But Putin stole it back because he could.