OK, so my mage has a 5 in each technique, a magic theory of 5, an intelligence of 2, inventive genius, and lives in magic aura of 5. Thus he can learn any L10 spell in one season. He has affinity with Magic Theory and is three points away from Magic Theory 6, so I am looking at inventing a Level 10 spell and putting the two exposure experience into Magic Theory, it becoming 3 experience and leveling Magic Theory.
Inventing a L10 spell is not the only choice. He could refine vis, or build a charged item, but since he is incapable of casting spontaneous spells, invented spells are extra useful. Inventing two L5 spells might also be useful
He already knows the following L5 spells
Clear Sight of the Naied:
Sense the Nature of Vis:
And the following L10 spells
Sight of the True Form
Lamp without Flame:
Aura of Enobled Presence:
The Call to Slumber:
The Crystal Dart:
So what other low level spells jump out at you as being especially useful.
Note, for General Level Vim Spells, once Magic Theory is up to 6, and with a Vim of 9, he can invent L15 spells in one season. So, while there still is a point in inventing a L10 Demons Eternal Oblivion, inventing a L10 Opening the Intangible Tunnel is a waste.