I live smack in the middle of a major wine producing valley, and work part time at a small winery now and then, so I have been to a few dozen wine festivals in the past several years. There are things I like about them and things I don't. As a participant, you usually get to taste some very good food, already paired with good wine, and you get to sample from wineries over a few hours without having to drive long distances. Once you see what it is that you like, then you know which wineries to go to in the future for more in depth samplings.
What I don't like is one aspect of the "festival" part. That is, a lot of people don't come to taste wine, they come to drink it. After four wineries of tastings, very little "tasting" is going on (usually given away by a person's purple lips) and drunks in any libation are not much fun for me to be around.
I have been to wine festivals before and I have always had a good time. Wine festivals usually have an incentive so that there is always a designated driver. This person usually gets some kind of bracelet that they must wear. This bracelet identifies them as being the "sober" one, this way they are not served any alcohol. Many times they also get free soda or water.
The atmospheres at these kinds of festivals are usually very relaxed but they can get quite crowded. There are definitely many wines available to sample and most merchants take credit cards as well. Some of the more popular wines sometimes sell out early.
There is an annual festival at a local vineyard in which women can re-enact the I Love Lucy Show: They climb barefooted into the vats of wine and trample the grapes, making juice. It is so much fun to do and to watch others as they sometimes fall into the grapes. In addition, there is usually a jazz combo that plays later on as people set up their chairs and tables for cheese and wine. Of course, there are the vineyards' wines to taste and a beautiful gift shop from which to select wines and make purchases of various items.
Usually, people do not get drunk! The wine festival is an opportunity to share good food and wine, and hang out together. There is cheese and bread too. I am referring to a wine stroll, which is basically the same thing I think. I like the idea.
I would make sure that you have a designated driver, Sometimes just "sampling" the wines can sneak up on you. A lot of the festivals will have entertainment that goes along with the wine tasting. Also make sure you sample the cheeses.