Don't run copper plugs unless you need to. They need to be replaced more often and often are accompanied with a poor idle. I'd go back to double platinums if you have no intentions of modding.
As for the drop in boost, did that happen before or after the spark plug change? What about the check engine light? If it happened immediately after the plug change I'd suggest looking at the vacuum lines going to the boost bypass valve. It's possible you pulled the vacuum line off of the valve. Plugs themselves should have no bearing on boost.
