You could use a schraeder valve tool to remove the valve temporarily while you have the pressure gauge connected. Some such tools look a bit like a radiator key but with a forked end.
That's a good idea! Certainly worth a shot before splashing out again. I'll just make sure to do it from cold ;)
And yes, I'm having some weird starting issues from cold. Warm restarts are 100%, cold starts take a lot of faffing about. It seems to start much more readily if I run the fuel pump between start attempts so I thought I'd better measure the fuel pressure and see what's going on at the rail.
From cold it cranks, stumbles, stops and after I run the pump I've got about a 50% chance on each subsequent crank of it stumbling again, or starting as if nothing had happened.
I've had some misfire issues last year so I replaced the coil packs, plugs, and wires which seemed to sort it out. Then the issues came back with cold weather and gradually spread to all the time. I have the odd misfire code (unsurprising) and the occasional serial link error for the antitheft but they occur far less regularly than the starting issue so I'm not sure if they're related or it's a multi-factor problem. The fun continues :)