When they state "Over 1 MILLION XP", does that mean you will be instantly rewarded with a lot of XP once you upgrade to members? Or are they referring to new quests and other means to achieve more XP?
As the Sizzling Summer FAQ says,
Those two bonuses are combine to make the "Over 1 Million XP" reward that you refer to. The FAQ also says that this XP will be delivered by a promissory note:
So, the XP is a direct reward for membership, with almost no additional action required on the part of the user.