Yes, this is the dilemma that eventually is faced by every successful vermicomposter!
Well, what we do is we keep "splitting the hive" all the time, and our collection of bins grows and grows. We started taking 5 gallon buckets, drilling holes in the bottom, and making mini worm bins in those. Then we sell them at local plant sales and things like that. It's a great way to get others introduced to the worm composting thing because they can take the bucket home and they are already in the worm business right away.
We harvest the worms by exposing the vermicompost to the sun. Then we scrape away an inch or so of compost until we find worms, then we stop. Then a while later we scrape again and then stop. Basically we're chasing the worms to the bottom. When you get most of the compost scraped off, you're left with just worms and a thin layer of compost in the bottom.
Some bins we make and fill, then just let the worms work it until the entire bin is solid compost, then we just wait for the population to just kind of die out and then use the whole lot as compost.
I'm of the opinion that you can never have enough vermicompost. You're really just limited to the space and containers you have and the amount of cardboard you can obtain.
