The Prestige Class Metaphysical Spellshaper (BoEF, p.81) has the ability to spontaneously cast metamagic spells, at the cost of suffering 1 ability damage per spell level the metamagic improves the base spell (and all the damage must be to the same stat at the same time).
The easiest way to go about avoiding this would be a Restoration spell (though it requires an additional DC 20 caster level check), but that only appears on the Cleric and Paladin spell lists. Going 10 ranks into Rainbow Servant is an option so you can cast Restoration on yourself, but it requires a lot of time and leveling. Another would be to carry a couple of Rods of Bodily Restoration (MIC p.173) or Orbs of Mental Renewal (MIC p.167). But is this the most effective way? Or are their other ways to do this?
Note: Books allowed are the BoEF itself and all the D&D 3.5e works. I'm looking for preferably a spell, but a magic item can also work. And no, convincing another party member to prestige into Divine Prostitute (BOEF, p.88) or haul one around as a follower is not an option.
Best Answer
Strongheart vest provides “Ability Damage Reduction”
The strongheart vest soulmeld from Magic of Incarnum reduces the ability damage you take by 1. Requires the Shape Soulmeld feat, which requires Con 13. Which anyone should have that isn’t undead.
Naberius, the Grinning Hound provides Fast Ability Healing
If you have a single level of the binder class, you can bind Naberius, the Grinning Hound to get the ability to heal ability damage at a rate of 1/round instead of 1/level.
Rod of bodily restoration is the most cost-effective item to heal ability damage
The rod of bodily restoration from Magic Item Compendium has 3 charges per day, can spend 1-3 charges to heal physical ability scores. Does not work for mental scores.
That said, metaphysical spellshaper is a ridiculously broken class
Metaphysical spellshaper is like an incantatrix on crack. Incantatrix, one of the highest-power prestige classes in the game. And you could have levels in both. I strongly recommend against playing this class. It is not well designed, and you will be vastly more powerful than almost anyone else could ever be.