The reason that earthworm castings are so good, is the huge range and numbers of beneficial microbes which come from a worm into their castings.
It is my opinion that this makes it an invaluable ingredient for a bacterial actively-aerated compost tea, whereby the numbers of these bacteria mushroom.
They do not last long at that level in the soil, but for the few hours that numbers are raised, it is my belief that they make enough extra nutrients available to plants to see a difference overnight.
It also means a normal presence of any of these bacteria missing from the soil.
In my view, this makes worm castings go much further, and a better economic choice.
There are many "recipes" for a-a ct, just add a couple of handfuls of castings to the brew.