The M:tG cards look awesome! I don't play / collect them myself but my understanding is that $50 is reasonable for a card that's available for less than a month.
Hasbro previously made at least one M:tG Transformers card (Grimlock) and that card goes for around $100. They also made ones for Nerf and Dungeons & Dragons. So I'm glad to see MLP join the ranks.
I hope they make another toy-related card every year! Mr. Potato Head, Care Bears (? does Hasbro have that these days?), Hungry Hungry Hippos, the possibilities are endless!