When the Serenity crew received a massive payday in the comic series Better Days, Mal subtly arranged for the crew to lose it because he feared that their independent plans for the money would break the crew apart. In this case, by contrast, the crew's successful payday from their time with the Enterprise will basically serve to bring them closer together as they're paid in raw material rather than paper currency, which they have to launder more carefully than they would when working with standard cash, to say nothing of the secret of their contact with the Enterprise bringing them together as they literally can't share the story.
Q's reference to him basically being under observation by the Continuum may foreshadow him being temporarily stripped of his powers in "Deja Q". When he used this latest "test" of the Enterprise to bend the Continuum's rules and simultaneously test humanity while cleaning up one of his past mistakes, it's not hard to imagine that his actions here prompted the rest of the Continuum to deal with him more decisively. It may also account for the Enterprise crew being relatively tolerant towards Q in "Deja Q" when his last televised appearance introduced the Borg and killed eighteen people; in the intervening time, Q not only brought those people back from the dead, but gave the crew another test where Picard has to concede that his opponent had a valid point rather than just talking down to humanity.
The destruction of the Reaver's Fleet is an excellent visceral showing of why the Federation keeps the Prime Directive so sacrosanct, and why they do not break it lightly. The Enterprise destroys an armada of over three hundred Reaver vessels in under a minute. It's preferable that someone with that sort of power take it too seriously than not seriously enough.
