Accidental Aesop: It's meant to be about listening to your friends' advice, but becomes more about the importance of explaining yourself properly, given that Pinkie never even tries to explain why she's looking for musical instruments.
Or warn the others, upon seeing the first few parasprites, that they're bad news. Or explain that she IS trying to solve the problem, at any point. There were a lot of opportunities for her to have explained herself. Oh, Pinky Pie, you could have saved everybody a lot of trouble if you weren't such a Genius Ditz.