A little late on the post, but I want to add to the discussion.
Personally, Vanilla fantasy is composed of the regular Tolkien races of Humans, Elves, Dwarves, Halflings playing often “Good” races with monstrous humanoids like Orc, Goblins, and similar races being the antagonists/baddies. Big creatures like Dragons, large scale battles, and a feudalistic government system appearing across the world can also be found in the milieu of vanilla.
I personally think Vanilla (both the ice cream flavor and the flavor of fantasy we are discussing) is dependent upon the group and game in question. For my own group and the Weird West game, I am running with them; it features your Tolkien races, but also Androids, and some anime-styled humanoid races with guns, cowboys, and magic thrown into the mix for good measure. For me and my group, there is enough Vanilla Fantasy and even Vanilla Westerns present to help new players coming into the group to play adjust to the game, but there is enough other flavors injected into the mix to make it different from my other games.
Similarly, when I began planning for a Gangbusters B/X game, I found myself first establishing the tone and feel of the genres of Noir and Hard-boiled Detective type stories before I began injecting my own milieu of Vanilla Fantasy and anime trimmings to both help get my players into the possible game but also help slide them slide into the game since they’ll have a handful of threads to hang onto at the start of the game.
I think the inclusion of Vanilla Fantasy even into some of the Wacky/Punkish style of games provides an easy thread for both rookie players and veterans to slide in and out of different games since the common thread vanilla fantasy provides is easy and simple to grasp. I think it’s how you can inject other flavors into the Vanilla is what makes things interesting.