Do the improvements touted by the ZPM Nocturn (PID-controlled espresso machine) sound sensible?
Speaking as someone who's built a few control systems, sure, a PID controller is almost always better than a simpler control system, but it's not a magic gizmo that automatically solves all problems.  I'm not familiar enough with how commercial machines are made, so I can't judge from their pictures and writeup how much difference their "improved thermoblock" is going to make.

Looking at your previous "troubles," I'd say the first step is to find a way to get good, fairly freshly roasted beans, grind them right before making espresso, and maybe get a slightly better machine.  No temperature control algorithm is going to make up for lousy beans.