Spartan Mora regiments at Battle of Plataea

[Giannis K. Hoplite]

it would suggest, if true, that it was not plucky Athens deciding to resist Spartan hegemony, but perhaps plucky Sparta throwing the dice against the encroachment of mighty Athens...

I thought that was the common notion!It is even Pericles who suggests that it is Athenians themselves that provoked Sparta with their Hegemony and their power.
It is made clear in Thucydides that Sparta had more man power in land,together with better quality,but it is also clear that Athens wasn't touched to a great extend by it. Again Pericles is put to speak in his "Epitaphios" as if Athens is so powerful that mere old style hoplites can't really harm her.
In much of the war Sparta and her allies are presented struggling to catch up with Athen's actions. And of course we don't even mention resources!
I won't elaborate more,since i am a bit off topic,but Sparta was indeed reacting to Athens' overgrowing power.it wasn't that powerful Sparta wasn't letting Athens reach its own level.
Another fact is that it is by far more the Athenian hoplites who are operating in the war than Lakedaemonian ones.
Khaire
Giannis