Most of the good defensive crew are best with one agility, or simply don't care.

Flight Instructor seems to improve with agility, as it has an increased chance of him going off.

Against ships with PS 3 or Greater, you may re-roll 1 [{Eye}] result.

Against ships with PS 2 or Lesser, you may re-roll 1 [{Eye}] or [{Blank}] result.

Against ships with PS 3 or Greater, you get 28/64 * 3/8 extra evades.

Against ships with PS 2 or Lesser, you get 55/64 * 3/8 extra evades.

Against ships with PS 3 or Greater, you get appx 1/6 extra evades.

Against ships with PS 2 or Lesser, you get appx 1/3 extra evades.

Is 4 points worth a crew card that gives you a free additional Evade result once every 6 times you're attacked? How about once every 3 times?

Only being able to reroll eyeballs against PS3 or higher really hurts Flight Instructor (its cost and competition for the crew slot don't help either). Unless you are being focus fired, Recon Specialist is going to work out to be a stronger defensive value.

The only times I could see Flight Instructor maybe being worth the cost is if you are planning on facing multiple low PS ships and are pretty sure you won't be getting many actions.

It comes even with rec spec at roughly 3 attacks per round (against 3 attack dice). this assuming rec spec always gets their action.