Don't forget the Sorcerer's Ring / Latent Set. They're cheap as dirt these days and you can build the set required to force your latent with extreme ease. There is a -lot- of 'converts 70 hp to mp' gear available for dirt cheap these days. I built a set last night without any ra/ex gear for approximately 200k gil, including
the price of the Sorcerer's Ring itself. Also, I have HP merits from my melee jobs, so for a dedicated mage it'd be even easier.
I can't think of any situation in which I'd choose 7 INT over 10 MAB.
Other handy but niche stuff (YMMV):
Fast Cast gear. Swap it in at the start of a spell, swap it out before it casts, your spell will cast faster and you won't lose potency since your damage is calculated upon completion. You don't get recast reduction this way.
Haste/Fast Cast gear: For drain/aspir/stun. Put this in any slot which isn't full of 'dark magic' gear to get your spells ready faster.
Idle Set: Refresh, PDT, stuff you wouldn't cast in but which is handy to wear. You might wanna have a "PDT Mode" macro if you're worried about getting your swaps all tangled trying to fulltime it.
Some dark skill gear for drain/aspir, such as: AF pants, dark torque, relic hands, etc
I used this for Stun too. It really does seem to help with the duration. Back at 75, it was the difference between those '...is no longer stunned is stunned' results and a solid 5-8 seconds of stun. Can't say for 99, I have not built all my sets back up on this new character.