Sacred Band of Thebes

[Paralus]

Plut Cleom. 3.1
But at the death of Leonidas Cleomenes came to the throne, and saw that the citizens were by that time altogether degenerate. The rich neglected the common interests for their own private pleasure and aggrandizement; the common people, because of their wretched state at home, had lost all readiness for war and all ambition to maintain the ancient Spartan discipline;

Plut. Agis 5.1-4
And here I may say that the Lacedaemonian state began to suffer distemper and corruption soon after its subversion of the Athenian supremacy filled it with gold and silver [...]. For the men of power and influence at once began to acquire estates without scruple, ejecting the rightful heirs from their inheritances; and speedily the wealth of the state streamed into the hands of a few men [...] Thus there were left of the old Spartan families not more than seven hundred, and of these there were perhaps a hundred who possessed land and allotment; while the ordinary throng, without resources and without civic rights, lived in enforced idleness, showing no zeal or energy in warding off foreign wars, but ever watching for some opportunity to subvert and change affairs at home.

The statement about the rivulets of silver tumbling into the Eurotas is almost assuredly true. The "subversion" had begun during the war and continued apace. The movement away from the "Lukourgan" provisions was well underway during the Peloponnesian War. The result only gave it impetus.