Very true, they aren't offered for direct sale. Something that I find really interesting is that if you look at say the prince for 100, it is 31.5 diamonds each for RR spells. KP are now 25 diamonds each. I've always thought KP were grossly over priced, to the point that it is insanity to ever purchase them.
Anyway, I bring it up because I can see that if you want to upgrade a building and you need the RR spells, well, I'd spend some diamonds sometimes just to be able to upgrade now. I want to keep my evolving buildings and I like them to be fully upgraded.
Consider an AW level requiring 1150 KP, that's 28570 diamonds for a single level... Those same levels that they've slaughtered with the new tournament design. Anyway, checking out how many diamonds I'd have to buy to do that, well, the closest with enough diamonds is the $199.99 diamonds package for 30000 diamonds, so there'd be 1430 diamonds left over, about 4.8%, so seriously, about $190 for a single AW level based on the current KP pricing.
It is just my thinking, but if you actually want people spending money on KP I would tend to think the price should be around 3 diamonds for a KP. That would be 3450 diamonds for that same level, which is still expensive and to me crazy to spend money like that, but for the say $49.99 diamond package you could purchase 2167 KP and do the better part of 2 levels, depending on the AW level. At the very high AW levels it is like 1 AW level.