I think one of the major things that have to happen here is the person considering the change to coil overs ought to ride in members vehicle to determine if the set-up is delivering a rid suitable for that person. I have been in a number of coil over equipped vehicles and it really depends on springs and dampening to make a difference. For instance a number of my fellow enthusiasts have coil over on their E39M5 and one of three that I rode in rode really nice like a factory setup but with better handling. The other two were stiff like a go kart and there is no way I would be able to live with that set-up on daily basis. The difference between the E39M5 with coil overs that I liked vs the other two simply was the spring rates and dampers/dampening set-up. With regards to the E53 if the air suspension system is functioning correctly and dampening as designed then the ride is acceptable to many. Many of todays cross overs and SUVs use full air suspensions to achieve a balanced ride and load control. So these systems have their merit but when they begin to age and fail then the nightmare sets in. If the air suspension in the E53 is failing, you do not want to waste time chasing the problems and you want a reliable alternative then perhaps the coil over is the way to go. Its a set it and forget it system.