Nice overview Steve.
I tend to agree with you and think the Spartans not yet at their peak post Plataea. Their later performances were many and varied and perhaps in the sense they had lost their aura of invincibility by the end of the Peloponnesian War - they still won with a winning strategy of dominance on land AND sea (albeit backed by Persian money).
...there's alot to the Spartans post Persian Wars up to Leuctra and the pending end from then on...
Cheers
Happy Wanderer