I dunno if anyone's done this yet, or even if it's allowed, but... well, here it goes...

Come to us, in times of leisure
Does this suggest that you do it when you have some down time? A sidequest perhaps, since it's been stated that it doesn't have anything to do with the main plot.
Don't be blinded by the treasure
There's more treasure than what the riddle is about.
Maximising your potential
Getting some sort of experience. Leveling up maybe?
thrice from seven, quite sequential.
You've already stated that this means 9. IX maybe, as in the game itself? I don't know what that would do with anything though.

Found by the nimrod that arrived
A nimrod arriving at Lindblum, hmm? Was it Quina when the party takes off for Kuja's fortress in the ship?
In home of minds which us contrived
For the life of me, I can not figure out what this means.
then headed linearly forth
Straight line?
four times, though still far from the north.
Far from the north, sooo... south?

I realize now that doing this is more confusing than the riddle itself, but I'll leave it incase this opens up more clues. Having said that, is anything right?