Yeah I want to be able to go in to both parks, I called Disney ticketing but he said I couldn't get a blackout pass since it cost 45 and my voucher was worth 72. I was a little confused, he did however say I could use it to upgrade my annual pass to the next level as long as the price difference was greater than 72. I think I am going to try calling them again tomorrow since none of that really made sense.
Basically - you can go to the park on a AP blackout day and buy and redeem your voucher for a single park ticket for that day. You could also upgrade your AP to a level that has less blackout dates. The voucher itself is worth $72. If the upgrade costs more than $72 you can use your voucher to get $72 off the price of the upgrade and just have to pay the difference out of pocket.
I'm planning on upgrading my hopper to an AP towards the end of my upcoming trip. We are there for 8 days and can only get a 6 day hopper. The majority of our time there is blacked out so we will wait to upgrade til later in our trip. the upgrade is $84 so our voucher will take $72 off the upgrade price.
Good luck with your dilemma. Hope this cleared it up for you a bit