DD10 and I live locally to WDW - we do both pin trading & autograph collecting.
Pin trading is fun, and if you plan ahead, and find some "lots" of pins on EBAY from reputable dealers, you can save some money. There are also some off site stores that sell Disney pins (and I believe Disney Stores - I don't go to the mall often, and have not been in a
Disney store in 4 years!) and I think they are a bit less - I had to buy some for DD on Sunday when I realized we forgot her trading pins they were $5.95 instead of $6.95+ - so I saved $4.00. PM me if you would like me to share some of the dealers I have dealt with and had good experiences. I recently bought a lot of 10 "mystery" pins all guaranteed to be official Disney of course, just did not know what they would be -for $35 inc shipping - so that made it $3.50/pin.
If you are doing pin trading its fun to try and find sets of CM lanyard pins that are available - we spent one day looking for the Disney bus set - we finally got them all, another was for a set of Coffee mugs with characters on each, or have your child pick one theme, or as I am sure most kids do - they just trade for whatever they like.
DD started that way, we would wind up with no pins to trade because she liked them all! Now she trades 90% of the time only for Chip and Dale pins. That does mean that we talk to lots of CMs and don't trade with them, but it's like a treasure hunt each visit! Sunday we went with 4 pins to trade, and came home with one new Chip & Dale, one Simba (another favorite) and I can't for the life of me remember what the other two are!!
As for autographs, we have books and books, and yes we have some characters multiple times, but in many cases it was a different location, and a different outfit - I am as much (or more) about the photos as the autograph. Now we try and find the rare characters we don't have, and yes sometimes she tells me CHARACTERS ARE BORING. We almost always have to visit Chip and Dale if they are out! I went a step further with the Chip & Dale theme, and made a small photo album of all the photos I had with Tara and "the boys", I made 4x6 photo cards for each character with a clip art, and had them sign that when we were at lunch at Garden Grill on Sunday. Each location that we had photos also had a "title" page with a clip art to separate them. "Dale" in particular took great interest in the album and spent about 10 minutes at our table (we were there at 11am - one of the first tables to be seated) looking through the books and gesturing about the photos. DD is 10 and these are really that only characters that she will interact with this way......