It can be worth the trip. They sell stuff from the parks (official stuff) thats old (from the last year or two) at a very cheap price. When we were there earlier this year they had WDW2002 photo albums (I think the sticker was 12.99 or even higher) for 99 cents. Unfortunaltly I needed 2003 or 2004(of course) but I bought 2 of those (2002 ones) back in 2002.
The also sell imitation stuff (ya know "disney" shirts that are actually iron ons that wont last long, like all that hillfiger stuff you see, there's some cheap stuff there, but you get what you pay for)
BUT, they also have a few items that are exactly the same merchandise that is at WDW right now and it's close to(if not) half price. Last year it was the spinning light up message signs(hand held, different messages can be read when you twirl it in your hand) they were something like 12.99 in the park and If I recall correctly 4.99 at the store. And this year I was at the Emporium and passed on an ESPN/Walt Disney World hockey jersey. I really liked it, but it was 35 bucks and we were late in our trip (had spent alot of money already) but then they had the exact one at the character corner for 18. It was the only thing we bought there this year, but it was worth the stop.