I do a fair bit of fermenting. I make sourdough bread, yogurt (both cow and goat milk), kombucha, and various kinds of fermented veg such as sauerkraut, fermented tomatoes, tomatillo ferment etc. One of my favourite things to make is goat milk yogurt; the milk is inexpensive while goat yogurt is very costly here, so I end up saving quite a bit. I recently got the River Cottage Fermenting Handbook out of the library, and I plan on making quite a few of her recipes. (I can't wait to make her fermented veg stock paste!)
Recently there have been numerous health claims around fermented foods, and I do think fermenting renders some foods more digestible to some people. A case in point is my friend's daughter who can't eat regular bread, but can eat my sourdough bread that has had at least 15 hours of fermentation. Also, there have been people who feel better if they drink kefir, especially goat kefir, and I've seen one study in which kefir increased diversity of gut bacteria. My own opinion of fermented foods is that they are very tasty, have been eaten for many years in many cultures, and are often plant based. Eating a wide variety of plants is good for gut bacteria, so if fermented foods help me do that, I will continue them. I personally do not see them as a "cure all", but I think they are definitely worth trying since there aren't any downsides to them.