And in the end "that other game" got rid of those effects as people were ignoring new gear in favor of old gear because the bonuses on the old gear made the new gear worthless.
Putting things on a long time investment grind is a bad move. You would not only have to find and acquire the gear with the Ability you want, you then also have to equip it for a longish time to be able to use it.
FFTactics uses a similar system. You equip an item, it has an ability, after a while, you learn it.
Unfortunately, the items that had skills you need were often very very weak. Especially when you get a new character at a higher level, you needed to have that character suck for a long time before it finally got good.
While I'm all for discussion and brainstorming about making gear a bit more interesting, i am wholeheartedly against anything that causes a power rift between long time players and new players/alts. Which is what your proposal would do.
Not only that, but you'd be forced to wear much weaker gear for a while even when better gear is available to you, simply because you haven't finished spirit-bonding it, but you would need to finish spirit-bonding it in order to have the skill for the raid which you cant do because your item level is too low to put out the required damage/healing etc ...
I think the Materia system has promise for letting us customize our gear a bit. (Obviously changing the way Materia slots are handled) Example:
All gear has a Primary stat on it, these can't be changed.
But we get 3 Slots in which we can put Materias that grant stats based on the item level.
All gear starts with the Materias equipped providing what SE feels is a 'baseline' stat spread for any given tier of content.
We can then choose to remove the Materias and slot new ones in. So i could take the Orthodox Tunic of Striking which has:
STR 54
Vitality 60
Crit 34
DET 36
But i could, if i wanted to, remove the Determination, and replace it with Skill Speed, Or another Crit Materia at the cost of -x% for each duplicate Materia.
So essentially, all gear would have a "Square approved" baseline stat spread, but we players can shift around the stats for what we want. Or think we want. It'd be up to SE to ensure that DPS numbers wouldn't get out of hand by giving us the customization, But i think it would scratch the "interesting stats" itch that some people have while changing nothing for those that are happy to simply take the gear they're given.