I use my VR lenses all the time, and it makes a big difference on handholding. I'm a firm believer in Sigma and Tokina as well, but Sigma makes a better vibration reduction system than any other 3rd party manufacter.
BTW - You should save up and get the Sigma 200-500mm f/2.8 as a natural match to the one you have now - It's only $26K. :-)