It's one of my pet peeves of Moff's tenure, way too many unanswered questions, eg, we see Amy's parents... and then they promptly vanish again. Or "Silence will fall" Or the TARDIS exploding. He's too distracted by the next shiny thing.
I agree with the point, if not the first example. Amy's parents vanish because they're not important again.
What point was there in showing her parents? We saw they returned to the void, and her childhood with them had been restored, why would we need to see them when Amy was an adult after that? This is no different, IMHO, then a Companion leaving, and seeing them again.
Now, about the TARDIS explosion, yea, if he's done with that, and not planning on revisiting it as an open mystery, then, that's certainly a legitimate gripe. Though, he may yet revisit it. We were just introduced to The Great intelligence, an enemy that hasn't been seen since Troughton's era, there could be a great big arc tied to the Great Intelligence (It could be behind the Silence, The exploding TARDIS, The Mystery of Claras, The Fall of the 11th....) I'm not saying The Great Intellignce is behind everything, but, it's not out of the question.