Fully agree and frankly its a pretty bone question. Pretty much every volunteer organisation has some sort of full-time component - the Cadets have a goodly tranche at County/Bn level, even the Scouts have a fair few. There could be an argument for thinning it out - but in order to do so it would take a HUGE change in the MODs penchant for creating nugatory paperwork.
I supose it depends on the unit and its role. My squadron supports a regular regiment, its PSI's are drawn from that regiment alone. The PSI's provide the essential link to the regular regt and without them we would not be able to fill that specific role. As for admin, booking courses etc I would rather see a NRPS/FTRS type who has greater availabliity since our PSI's, quite understandably, are often not available.
Is it possible to have a reserve force without a regular? Yes.
Is it possible to have a regular force without a reserve? Yes.
Is there an optimum balance of regular to reserve forces (force mix)? Maybe.
Does having a balance of regular/reserve forces allow the MOD to maintain a total force that takes account of the various issues associated with doing so, such as the demographic issues of specialist recruitment? Yes.
Are regular forces expensive? Yes, especially when you dont use them.
Are reserve forces expensive? Yes, especially when you do use them.
The permanent staff in TA units like PSAO's and SQMS's etc look after the administrative function of TA units like ensuring those that turn up get paid etc and clothing issue's.
It is the SPSI's however who are responsible for ensuring Tuesday nights, training and exercising weekends happen. Equipment is serviced and maintained, training areas are booked and everything else that is involved in ensuring these weekends and Tuesday nights happen is the sole responsibility of the SPSI's.
So perhaps the TA cannot function without its regular component.