Skill/spellspeed is good for exactly one job, BLM, because their class gimmick involves circumventing resource management, which is the entire reason why skill/spellspeed is not a desired stat to begin with (running out of TP too quickly). Additionally, it has exactly zero impact on damage over time spells, so it's worthless for summoners. Healers don't value it much because healing is much less about pumping out as much HPS as you can and more about choosing the right spells/targets, resource management, reacting quickly with clutch heals and so on.

Ultimately all the stat would need to make it a valued stat is to have it increase the rate of resource regeneration. However I have to wonder if this is even possible, since it seems like *everything* in this game works on the same 3 second server tickrate and it may not be possible to change this without modifications to the underlying architecture of the game.