We did it last Spring and it was good, not great. The tour guide was part of the gardening department and the best information she gave us came from stories from her real job, such as what happens when a freeze is threatened for central Florida. Unfortunately, there wasn't as much of this as we would have liked. Of course, if you are really into gardening and need to have each plant at EPCOT identified, then this is the tour for you! We also got a souvenir poster from the Festival, which was very nice.
We took the same tour back in 1995 when they used someone from the tour staff as the guide. We felt like we still got very good information (the trial and error involved in finding plants that looked like they were from Norway but would actually grow in Florida), but the whole presentation was better. Also, back then, the whole tour focused on World Showcase; last year, all of EPCOT is included, so it feels more rushed.
Also, the best discount on the tour usually is given if you charge it to your Disney Visa.
Best of luck -- Suzanne