NASA's SIM mission was recently cancelled despite \$600 million being spent already over the last ten years.
Has this \$600m been completely wasted or has any new technology been developed that could be useful in the future?
I don't know about any new technology specifically from SIM, although it's entirely possible there was some.
However, the money definitely wasn't completely wasted, as it was used to employ probably hundreds if not thousands of people during that time that were working on various aspects of the project from design to prototype fabrication to simulations and studies of exactly what could be studied and observed, as well as project management, facilities personell, etc.
Disclaimer: I didn't work on the SIM project but I am a NASA contractor. And I did know some scientists involved with it.
Also don't know of any specific technology from SIM, but supporting science and engineering is some of the best investment in the future that a government can make. The dozens or hundreds of junior staff that worked on the mission got priceless experience that will increase the nitty-gritty, dollars-and-cents value of their labor to the economy as a whole for decades to come.
Disclaimer: I also didn't work on the SIM project, but I am a junior staff member at a government research facility getting experience that will increase the value of my labor to the whole economy for decades to come. :)