Druids should have control over all things natural. I don't give a rat's anus about this whole 'creature/plant' association, it's moronic. The natural includes mountains, rain, the orbits of celestial bodies, whatever.
Shamans should have control over all things spiritual. Since there are spirits to represent everything, shamans should have power over all things through spirits as their proxies.
Magic is not meant to be restrictive, if it is, then it is just a profession - utterly meaningless, devoid of roleplay. It is suppose to be a creative endeavor. Sure, we should prevent people from powergaming, but provided there is reason to some shaman being able to repair a machine (by invoking a technology spirit) or a druid calling a storm (because it is natural and thus under the domain of the aspects), I see no issue with any of these things.
That said, I'd prefer it being written into the magic itself, rather than as adjuncts. These stones will probably just be sequestered away, never to be used, in all honesty.