I do the same thing. Honestly, you're doubly-smart because you're saving money and time. My kids take forever to pick out souvenirs, especially when they're tired.
Like you, I still buy a few things at the parks themselves, but they're things you can't buy elsewhere, like embroidered mouse ear hats, Mickey-shaped earrings or Haunted Mansion pins. I also save things from trip to trip - my waterproof bag, croakies, and ponchos get used for every amusement park. We have light-up "crystal" necklaces ala "Disney's Atlantis" that are ancient, but they're in the bag. When the kids were little, if a dark ride scared them, they'd just press the button to see the light and get distracted. Now, the kids
jokingly make a fuss about getting them out before we enter the Haunted Mansion, lol. They like it when other people waiting notice and comment about their necklaces. (Attention-seekers, aren't they?) I think they also remember how that little light kept them from being too scared. (Note to self: never let oldest DD take a newbie through the HM. sigh She's so mean!)
I picked up Disney t-shirts for my kids at the Kissimmee
Walmart a few months ago. I wasn't really doing it to be stingy, they were really cute shirts for the summer - fitted for girls, with printing that matched their personalities: one was a little bit punk, another had butterflies. I told them honestly that I didn't buy them IN WDW, but I thought the shirts were perfect for them. They're too old for Disney Princesses or Fairies, so this fit the bill. They wear those shirts at least every other week!
I always forget about the light-up stuff. I really like seeing all the glowing, spinning, lights at the parks - it's so festive. We rarely buy those trinkets because they're so expensive. That's a good suggestion to pack them away because they're so easily broken and they're expensive. I always buy inexpensive glow necklaces from the dollar store and then forget to take them with us, too.