MiSSi, what i reckon is, it all depends on what you want to do.
i want to make it into a certain university course. i need a certain uai to make it into that course, and my uai just so happens to be about 20 uai points away from that.
my uai is in the low 60s and i think with this number it will be hard to get into ANY uni course, and when i do, it will be hard to transfer. so the option of repeating year 12 looks good. that way i can get another uai, if i actually did better in school, i might be able to get the mark to go STRAIGHT into the course i want. that's the plan.
i've heard about people getting a LOWER uai after repeating. so i reckon it depends on you.