Since you already have base tickets, you'd be fine to still visit the parks on the same day as MVMCP. You may just want to stop a little early to get some rest in before the party.
This is how I see it. For us, I think it's fun to sometimes do things for the adults. Will our youngest, who will be 2 in December, remember the times she went to MVMCP at 2 months old and 14 months old? No, but we will remember the fun we had and the pictures we have of her.
Plus, she was free to get in! So why not enjoy the party for yourself while at least one of your children are free to attend? I figure that even if our children fall asleep, at least we experienced it and we can decide to do it again in the future or not. As far as I'm concerned, I like to enjoy as much as I can while our children are still free or charged at reduced rates.
Ticket prices only get more expensive as they get older!