Actually Theramore brings two unique items that will disappear come MoP. For the Alliance - a Theramore tabard that has a "plant Theramore banner" on use effect and a Mana Bomb fluff item for the Horde, with a 30 min cooldown that I'm honestly not too sure about its effect, since i'm Ally, but assume it does a pretty big blue explosion.
When MoP comes out these two stop dropping.
Also Blizzard's stance on this event is that they preferred keeping their resources into MoP content rather than "one week of events that will take a lot of time to prepare and be forgotten forever". Which I absolutely am in favor of.
Yeah, at first the pet wasn't in there. A Blue later clarified and now it's on the page as well. Looks like I'll be buying that then. :]
I've explored Pandaria a bit and frankly found it pretty sweet. The major lore isn't really interesting but the small lore, as per the usual Blizzard style, is very engaging. Also Pet Battles and all those small things I like about Blizz games.