It also could be she's worried that Spike is going through another greedy episode like he did in Secret of My Excess. After all if a dragon like Spike gets too greedy he goes Godzilla on Ponyville. Still, it was a bit of a jerk move.

@Platus
It was like a True-Meaning-Of-Christmas moment. She pretty much said that he should focus less on materialistic things and more on lasting things. The way she handled it, however, was kind of devious.
It's My Little Pony: Friendship Is Magic, not My Little Pony: Crystals Are Magic. (Unless you're Sombra.)