From what I see, the problem is not necessarily lack of motivated staff, but it's the practicalities of exercising the qualification.
Most squadron commanders I know want to run as many activities as they can in-house. Where a capability gap exists, they tend to make inroads with the nearest sqn that can help. I tend to work with around 4 squadrons. We have SAA staff, 1 has an air rifle range and RCO's, one has an SOV and AT staff, and the other one has got no staff, so we try to lend a hand by dishing out spare places. It's an unofficial sector, and it works fairly well. We barter for activities - "if you run an exped, I'll run a range" type of thing.
In my opinion, more should be invested in helping small groups of squadrons up skill amongst themselves. Shooting staff can do extra shooty stuff, and, in return, the sqn benefits from getting extra first aid or AT or whatever. Staff remain on squadrons, where they are most useful, cadets get activities, and the admin remains manageable.
There is a place for Wing assistance with activities - a monthly Wing full bore shoot, the odd Wing run SAA session etc. In my opinion, these should be there to pick up the slack, not be our main effort.
Of course, the other alternative is to disband squadrons, have wings as the minimum formation, with the old squadrons as flights - eg. "123 (Anywhere) Sqn" becomes "123 (Weapons Training) flight, East Somewhere Wing"