I’m squinting at the 1000gp/spell level cost of replacing a spell in repertoire with another.
I don’t have a terrific handle yet on the amount of loose cash higher level (say 5+) characters have, but during the lower levels 1000gps is a lot of money. It seems like it would effectively keep mages from changing their repertoires during the first few levels much at all.
What’s the design intention? What would break if changing spell repertoire was drastically cheaper or didn’t have a cost at all – merely the 1 week/spell level time requirement?
It’s deliberate in that the idea is to make changing the spell repertoire expensive enough that mages don’t do it lightly. The concept grew out of a dissatisfaction with 3.5-style wizards who had an answer for every problem with a night’s rest. Since ACKS mages can free-cast without memorization, it’s really generous to let them change their repertoire at all 
That said, the 1,000gp/spell level cost is purely “fantasy” - it doesn’t break any of the economics per se.
If you want to help out low-level wizards you could say
120gp for 1st level
600gp for 2nd level
3000gp for 3rd level
4000gp for 4th level etc
or something like that.
Thanks for the detailed answer.
What about dropping the GP cost and keeping the extended time period of 1 week spent in an an arcane library, becoming reacquainted with the spirits, signs and taboos for the spell being swapped in?
I'm sure that'd work fine. Less of a gold sink, but ACKS has plenty of gold sinks.
If you try it out, let us know how it goes.