I completely agree with
@BDFmom
Even though I haven't done either

We are doing 1 EMM and 1 MVMCP. I stalked the EMM release for December like a hawk. I thought I struck gold with this new event!! lol! And that is actually one reason why a second EMM could be appealing.
It could be possible that the event isn't around "forever." I dont know how often new events are announced, and how common it is for Disney to remove them. But, it seems to me that MVMCP would likely be around for a really long time...
HOWEVER, I digress....I still vote for a second MVMCP....
I would love to have another party night. I would like the first to focus on staking out an awesome parade spot and not have to worry about my girls not seeing the rest of what the party has to offer. I'd spend the time up by main street shopping and enjoying the fireworks up there and any other shows..
the second night I'd focus on rides, grabbing some cookies, just walking around enjoying the sights, grabbing some cookies, maybe wait in line to see a character (probably jack ), actually sitting at a TS for a meal during a party!, grabbing some cookies and cocoa...
EMM sounds like such a cool opportunity. I'm definitely glad we're doing it. But, as you said, it is such a short event. I think if you can get fp for those three rides during some of your time at MK besides from your 1 EMM day it would be a good amount of time on those 3 big rides....unless your sole purpose in booking it is for the out of the world PPO breakfast at Pinocchio Village Haus; in that case you may need 2 EMMs.
good luck making your decision!!