Thanks for your comments Clinton.
You ask, "does your model take into account the fact that one of the benefits of IRPs is that outbound and transiting aircraft have known, identifiable points to avoid?"
The answer is no, my model it is not that elaborate. It could be further developed.
The proposal for inbound VFR lanes (marked on charts) might assist in this problem.
Re the closing of Westmead IRP - an idea - could it have been for controller convenience - they have an easier time visually scanning in 2 directions than 3?
You also say "I don’t see how restoration of Westmead would have avoided the recent MAC near TWRN". A short answer is that the numbers are too low for statistical validity in individual cases, and that it why we need a model so we can merge all the actual cases.
A second answer is the "push around effect" - closing Westmead forced traffic from the north around to PSP, and the increased density there led more traffic from the west to choose TWRN.
Regarding visibility of TWRN (and Westmead in the past) - why not place a strobe light there? (Could equally well help to locate an inbound VFR lane).