Although the Commonwealth was created with a good premise, I do not think it upholds a valubale and useful mission in the world. It has no say in economics or our security nor does it serve a purpose. Its an outdated system as well as expensive and should no longer be used.
Go and ask your average American what the Commonwealth of Nations is. I doubt you'd find anyone able to answer the question correctly (if you're interested, there's a great wikipedia page about the Commonwealth).
The fact that the Commonwealth is completely unknown in America certainly indicates that their mission is not being implemented very well. An objective of spreading peace and democracy is a great objective, but if nobody knows that you're trying to spread peace and democracy, you must not be doing it very well.