Spirit:
Mentalist - Spirit can be used to attack the mental stress track, and has +1/+1 when doing so. Lawbreaker is highly likely for using this.
Even at a power penalty (and no control bonus), this is really good (especially if no other elements are allowed to make mental attacks at all). I would include in it explicitly what skill is rolled to resist (maybe allow Discipline or Conviction).
I view this more as a "brain overload" rather than a "brain rewrite" so I am not sure if it is a mind violation (you aren't reading and you aren't making them do anything permanent, unless you inflict an extreme consequence--brain damage?). I think it would also be appropriate for Spirit to be better at "mental blocks."
But how are these abilities "purchased"? Are they like "take a refinement and get 1?" In that case Exploder is just way too good (even if it uses all specialization slots granted from 1 refinement), it basically says "Fire Zone attacks cost 2 shifts of power, but you get +2 power to compensate,
and give +2 control." Granted you have to do a zone to get it, but assuming this stacks with other specializations it is even better. Normally to get the equivalent from specializations requires Fire Power +2 and Control +2 (which means you have at least 2 specializations at +1). And again if it stacks with existing specializations then a character with Fire Power +2 and Fire Control +1 is getting +4 control on zone attacks. Even just giving "Fire Attacks may be upgraded to zones at no cost" for -1 refresh is good since it basically means that fire zones get a virtual +2 power (that stacks with specializations, while not adding to the pyramid's top weight).
It occurred to me that maybe instead there could just be more "buy upgrades."
Like you basically outlined a "it costs 3 shifts to add a non-sticky temporary aspect related to the element." Maybe allow additional shifts of power for more stickiness. The only balance concern is that this makes practitioners even stronger as they can apply an aspect AND attack in one action
What about a 2 shift exchange that lets you change the resist trapping (as long as it is related). Like air might target endurance as you pull the air from their lungs, water attacks might as it tries to knock the target over.
2 shifts to attack mental stress (again, maybe just allow spirit to do so, or charge more for other elements). Alternatively make it cost 1 shift for spirit and 3 for any other element. In that case I would probably charge Spirit more for Zone attacks (like 3 shifts).
2 shifts for the option to knock a target 1 zone seems balanced (I think before I talked about starting at 1, then increasing the cost by 1 more for each additional zone; 1 zone = 1 shift, 2 zones = 3 shifts, 3 zones = 6 shifts, 4 zones = 10 shifts, etc.)