Well I replaced my fuel pump and pressure regulator, put it all back together and... no improvement.
I researched the symptoms (not specific to any vehicle) and came across a site that covered fuel injection issues. The first one on the list was "difficult to start when hot". So I ordered 2 new IWP 189s.
Put them in today after work and she runs perfectly! Beetle's first suggestion was injectors and they seemed fine. I wonder if they behaved properly in my hand but then acted up when installed (compression, heat etc.) Anyway, she's all good now, and I'm much more familiar with her.
Many thanks for all the help!!!