I do think Haunted Mansion will be busier than the average weekend. Supposedly they're adding a
new element (click link for more information) into the attraction during it's brief closure this week. So I would anticipate some folks coming in to see what's new in the Haunted Mansion.
I do think the marathon will increase crowds in the parks and DTD on Saturday. I was there for the Avenger's Marathon weekend in November, and DTD was quite busy (although, it's usually pretty busy on a Saturday). If you have to drive into the parks, be prepared for a long line of cars getting into the parking structure.