Yeah, I'm not really getting the desire to shop in Toronto-area malls, either. The stores are going to be pretty much what you'll get in any US mall, and with the higher taxes you probably won't save much - if any - money, even at the favorable US exchange rate.

If you wanted to go to funky, independent, urban-boutique shops, then I could see taking the TTC into downtown Toronto and checking out the shops on Queen West, Kensington Market, etc. - those places would probably have lots of cool things you wouldn't find in IL (except perhaps in Chicago, but even still I'd say Toronto's got a much more funky/alternative vibe than Chicago, so the shopping reflects that - more cool stuff on offer.)

Otherwise, with a layover of that length, I'd just go into the city and explore. There are a lot of cool things to do in Toronto - great food, cool neighborhoods to chill out in, and the TTC makes it easy to get to and from the airport.