Since they're only selling Enchant and Imagine Keys, I'm not sure it's worth buying either right now. With the Enchant Key, there are only 23 total days left before the summer blackout, and with the Imagine, there are only 15. Then, both are completely blacked out until August 15th and 22nd, respectively. With the first anniversary coming up in August, and the Dream and Believe Keys still unavailable, I'd probably wait to see what news comes out over the summer, before sinking money into a Magic Key.
ETA: Enchant Keys are blocked out many Saturdays and Sundays, throughout the year, and Imagine Keys are blocked out Friday, Saturday and Sunday.