personally i think 16's look a lot better then 17's on the
ibiza if you lower it enough on 16's it looks right, the proobelm with 17's isn't the arch gap but the car body to floor gap, a lowered car shuld look lowered not be on stilts but with no gap between tyres and body.
i could have mine on the floor with with 8's all around on 17's. so the
problem with 17's isn't between body and floor, it's mostly the width that prevents you going any lower. my cupra's around 2" off the floor so i wouldn't exactly say it was on stilts, even for 17's. 1" smaller on the width on the rear, the wheel would tuck right under that arch. but the
ibiza's arch's are huge for a 3 door hatch!
2nd thing is being practical. I had enough headache snaking around speed bumps, potholes, ditches etc with my polo. it would be even worse on 16's. it all comes down to personal preference. but if i had it my way, it would still be 16's.