Alfred - I would argue that there is a demand in the chain to see "spare capacity outside of your primary duty". This rather implies that all primary duties are equal, which they certainly are not! There is also an implicit assumption that these are completely removed from your primary duty - someone who organises the summer ball gets extra credit, someone who sorts the squadron/force with extra warfighting capability with their spare capacity doesn't get the same recognition as it's seen as just part of their job.
Where secondary duties have a place is to allow someone to fill gaps in their report that they couldn't by doing their primary duty. We seem to have lost sight of that and have let the tail start wagging the dog.
Back on topic to the SDSR - I'd be very happy to see some focus on improving retention and serviceability of existing kit, rather than shiny headlines.