Rather than doing a new profile reading can I simply pull the RGB xy values from my spectro's probe match matrix readings for the screen and use those to create the new user colour space?
You can do either, or use the 'Modidy' function in the Library to auto-extract a colour space gamut and gamma.
Secondly, given that this seems to be quite a powerful method, is there anyway to automate the creating of the user colour space from a matrix/colourspace, given that all the necessary information has already been collected? Perhaps in Colour Space manager there could be a "convert to <whatever this is correctly called>" option that would take the necessary data and create a user colour space that could be used for reduced gamut profiling, which would remove the necessity for fiddly manual work.
See 'Modify' above...
Finally, is there an objective way to decide when reduced gamut profiling is appropriate for a display?
As explained in the User Guides on using Sub-Space, it is ideal to use what a display is pre-calibrated to a colour space it actually cannot cover.
Mob Boss at Light Illusion