The question of use vs. cost is down to whichever theory of accounting MoD choose to use this week. One thing that's for certain, however, is that if UK9 is purchased with a total lack of support - eng & crew manning, spares for deployment, tooling etc - (as per UK7&8) then all that we're buying is an extremely expensive spares donor...
The capacity and abilities that it brings to the 'customer' makes it ripe for the future, especially so given uncertainties surrounding A400s development timeline and current issues.