Again, this post more than likely comes too late to be of use to anybody already in this thread.
However, the decision depends on what you're going to do with this Crown Vic. If you like the automatic leveling and ride, go ahead and get air springs. If you plan to tow heavy things with it regularly, then I'd also have to suggest the steel springs.
Something you might like to think about.... If you're going to abandon the air suspension, it would take next to no work to remove the air lines going to the rear end from the compressor beneath the hood, and putting your own short metal lines with a quick-connect air socket attached. After that, you've got your own air compressor inside your car! You'd be the only guy around who could fill up his own tires anywhere
