Hello fellow Nebraskan!
The cost to upgrade to a park hopper pass is nearly the same as admission to Mickey's Not so Scary Halloween Party (MNSSHP). So, making the decision based on which is the most cost effective is pretty much no help.
And now, I must tell you I love MNSSHP. The chance to wear costumes as a family, to trick/treat at WDW, to see a one-of-a-kind parade and fireworks, to have the chance to not have big crowds (this varies with the day you attend, however), to meet many, many characters, to see Cinderella's glass carriage, and to see the Magic Kingdom even in "costume" is something I find so incredibly magical. You can certainly sneak a peek at what the evening looks like by doing a search on Youtube.
So, I'd spend the money for the tickets and think that one day you'll get the chance to park hop. Begin the day of the party at one of the other parks and then you get to "hop" to the Magic Kingdom to enjoy the party.
With visiting 5 days, you can spend 3 days at the other parks and still have 2 (and a half with the party) at the Magic Kingdom. If you do find that you need a break during the day, you can exit a park and return to it later in the day.
And remember, you are welcome to visit any of the resorts (perhaps for an afternoon snack?) and Downtown Disney with no admission cost.