Neil - You Asked -
Quite a bit, actually. Most of the realm of this question is not really relevant to the story at this stage. Much is back history - a curiosity that might bear examining for future (related) short works.
These stories have scarcely scratched the surface of Althain Tower's many and multifaceted mysteries, quite a few beyond Arithon's depth to handle.
Access to Althain Tower's fifth floor, comes to mind instantly.
Certain other of the Paravian artifacts in storage and safekeeping. Certain records and archives, at THAT point of Arithon's development. And as you saw, Rathain's crown jewels, without any masking spells to conceal their true purpose.
The old maps and navigational equipment served two purposes: permitted Arithon access to blue water sailing, which allowed him to escape the immediate effects of the curse AND - reviving the old arts of navigation would restore deep water shipping. This effectively took pressure OFF expanding coastal ports for galley havens, and took further pressure off the land based trade routes - sail is faster.
Therefore, by default, it lessened the pressure for townborn trade to develop and encroach upon the free wilds.
Canny guy, Sethvir.