Is pin trading as big in DL as WDW?
I would have to say that pin-wearing CM's in DL are definitely not as prevalent as WDW. When we were at WDW in April this year, it took us forever to get from ride to ride as my 7-year-old daughter absolutely had to check each cast member's lanyard that she crossed path with and there seemed to be a ton of them in all four parks. It was her first time pin trading and good thing I brought all my backup traders I got from EBay (I ordered 50, but only gave her 20, thinking that would be plenty, but brought the rest along anyway, as we were going on the cruise and thought maybe we could do pin trading onboard). She traded all 20 the first day at the parks! And she's fairly picky, looking only for Chip and Dale pins and CARS and Toy Story pins for her brother.
My daughter had high hopes to do more pin trading during our August trip to DL. We were quite disappointed. Definitely not as many CMs with lanyards hanging out in DL. We noticed especially that not many DL line-tending CM's and cart vendor CMs wear the pin trading lanyards which was how we got the majority of our pin trading done in WDW. DD ended up doing most of her DL pin trading during pin trading events at the Downtown Disney Oub Store, DVC kiosks and surprisingly, at Grand California Hotel where we stayed. We also noticed that DCA seemed to have more of the "desirable" pins than DL.
DH actually wrote to Disney management after our August trip about the need for more kids' only lanyards at DL. My theory is that perhaps DL employees on average are serving more guests per hour than WDW and they don't want to offend guests waiting in line to buy ice cream while the vendor CM chitchats with pin trading guests, which may explain why you find more cleaning crew CMs wearing pin trading lanyards than gift shop CMs at DL, compared to WDW.
Don't get me wrong, you can definitely find opportunities to pin trade at DLR, I'm just answering the OP's question asking for a comparison between DL and WDW.