First of all, Tyvek is one of the biggest building gimmicks ever put out. It does virtually nothing. It has no R value, and if your home is that drafty, you're in bigger trouble than something like Tyvek will fix. A good job with an elastomeric copolymer caulk will be much better. I would use the Styrofoam for insulating reasons, but make sure they use the metal bracing properly.