I had airbag on a SAFARI van before. It actually made the van ride better. air bag absorbed all small bump and take shock impact on large bumps.
It was a simple bag system to help load with lowered van. didn't have on board compressor so when it leak flat.. it is a pain to get the bag in the right shape again.
Air suspension have change quite a bit. It isn't a performance enchancing item. but more for show. so you can drop and jack up the car as please.
Since alignment is sensitve to ride height you will need to really set the bags at a certain pressure = Height.. align the car and then get the suspension at that pressure all the time to avoid bad alignment.
Good alignment is essential for tire wear and responsive handling.
for IS300. can't beat a great set of coilovers like JIC, Tein & Zeal.