I'd go a different path: the least crystal grants expertise when wielding the weapon (so you can change it from a rapier to a spiked chain to a maul to a Jovar greatsword to a minotaur greathammer to a ribbon rapier) and keep the property. Same for armor; though that would mean you could go anywhere from chain shirt to full plate in a matter of minutes, but since most of the light-armor classes already have abilities that depend on little armor, that means it would be more of a novelty than anything else.
I'd suggest a crystal of Finesse, upon which you can treat any one-handed martial weapon as a finessable weapon (but not two-handed weapons) for purposes of Weapon Finesse. That could open the Weapon Finesse feat for even more weapons (mostly longsword and scimitar which are the most evocative) than normal, but you would be essentially locking out other augment crystals (since you can only apply one augment crystal per weapon or armor).
I'd also suggest a Least, Lesser and Greater Crystal of Armor Adjustment. The lesser would decrease the armor check penalty of an item by 1 and increase the max Dex bonus of an armor by 1, the Lesser would be 2 instead of 1, and the Greater would be 3 instead of 1. Though, I'd personally go for -1 ACP/+1 Dex for Least, +3 ACP/+2 Dex for Lesser, and +5 ACP/+3 Dex for Greater. That way, you could make heavy armor and Dex-based characters an applicable option. I'd also add to the Lesser Crystal of Armor Adjustment that the armor does not restrict your movement (if medium or heavy armor) thus you can move at your base land speed and use skills like Tumble on said armor, and the Greater Crystal of Armor Adjustment would allow you to treat the armor as lighter for purposes of class-related abilities (heavy to medium, medium to light, light remains the same).