While Vancouver isn't traditionally an autumn destination (our forests are predominantly evergreen, after all), there are so many great autumn events that most people aren't even aware of. Two events that I'm particularly interested in are happening out at UBC. Both will allow you experience all the fantastic sites and smells of autumn.
Saturday, October 3rd
9am until 1pm
UBC Botanical Garden
October 17 & 18
11am until 4pm
The UBC Farm Harvest Fest would be a great excuse to get out and experience the only remaining true farm in the city of Vancouver (whose future is undetermined, as the farm's actually zoned for development, but is currently sitting in limbo - boo!). I've never visited the farm, but my Dad (who spent his childhood summers in Hay Lakes - ie: small farming town - Alberta) says that he actually feels like he's back in Alberta when he's there. It's apparently a lot larger than people anticipate. My sister, who works at UBC, says a visit to the UBC Farm is an absolute must.
The UBC Apple Fest is a lot of fun, in that old-fashioned country fair kind of way. I think they charge a small fee ($2?) for entry, but you essentially get access to the entire UBC Botanical Garden, plus you can do apple tastings, buy bags of apples - and we're not talking about Granny Smith's, but dozens of unique and rare varieties you typically don't find in stores. They sell apple pie, candied apples, apple cider, and there's usually entertainment. I visited two years ago and it was so enjoyable. Just be sure to get there early, especially if the weather's nice, as they actually sold out of many apples by the time we arrived.
I have nothing set in stone yet, but if I manage to make my way out to either event, I'll be sure to report back!