Oh yeah, forgot to update.
Well... It was all a bit strange really. In the couple of days before going to Pheonix, the car also developed a slight misfire, but only on idle.
So I got the car to Pheonix and Mark whipped the cover off the engine and promptly diagnosed that the engine breather system had been hosed incorrectly for starters. So he sorted that out, replaced a shot coil pack connector, and replaced the sparks.
Then he moved the vacuum hose going to #1, as this one was kinked.
And now it boosts just fine!! 1.2 bar is back! Which is really odd, because if the kinked hose to #1 was causing a problem, I would have thought #1 would have had trouble spooling.
Mark suggested that the combination of these other factors, while being no major issue on their own, could have combined to result in my car being unable to switch to #2.
These problems aren't black and white, are they?!