I did 5 seminars last week and if you enjoy wine I think they are definetely worth the time.
If you go on a weekend you'd definetley need to be there 30 mins ahead, during the week people were arriving less than 15 minutes before and getting in with no problem
We did a New Zealand, Italy, Rose, Argentina and Mission Hill seminar. You don't really know ahead of time what they'll be like as it varies with the speaker and wines. My favourite was the Mission Hill one, the speaker was funny and informative, I didn't know much about canadian wines other than ice wine so learnt a lot and got to try some fabulous wine.
The Argentina seminar was also really good. We got four wines at all seminars apart from the Rose one where we got 3 glasses, and they normally were a mix of red and white so to fully enjoy the seminar you'd need to like both styles of wine.
Overall the seminars were one of the highlights of my trip.