Although I do digital scrapping now, I used to do paper and have bought the supplies at WDW. I've bought stickers and page kits, never any books. Some of the kits and stickers are exclusive to WDW, so if you want things that are different, then get those. The trip to DTD exclusively to visit the scrapbook shop isn't worth it, you can find everything there at the parks and resort gift shops. And if you have the Disney Visa or AP discount, you can buy it at World of Disney for the discount. There are also some park/resort specific items that are only available at those parks and resorts, so if you want those you will need to buy those there, they won't have them at DTD.
It's worth it to get a few things, they will be extra special on your layouts, but get the bulk of your trip items from your home shops. I would suggest visiting your local shops and familiarizing yourself with what they have to offer (or the online shops too) and remember what you liked when you are shopping at Disney. See what items will enhance your other items.