The actual npk value varies by what is fed. Typically you'll see something near 1-0-0. That doesn't mean there is no phosphorus and potassium, just that there is less than 1% by volume. When compared to liquid ferts it may seem low on a surface level but again It's by volume. Some people mix their soil to have one third of it as pure castings, whereas in a typical liquid fert feeding you're using maybe 1/4 teaspoon.
The added pluses to castings is definitely the bio herd as well as improved aeration and its anti pest properties.
There are other trace elements in castings as well but a little help from amendments never hurt.
As far as your runaway worms... remember the worms are living things just like you and I. If they're unhappy with their living circumstances they hit the highway in a hurry.
Common reasons for them to high tail it are overly wet bins, bins that have become too acidic, and bins that go sour from too much food or unbalanced c:n ratios.