The difference isn't in the spring, coil or air, the difference is in the dampening mechanism. Air sprung forks are easier to adjust for a given rider's weight, you change the air pressure. While coil sprung forks may require to change you the spring itself. That and the fact that air sprung forks are lighter has gotten coil forks out of fashion for anything but gravity riding.

I think the RockShox 30 Silver wit coil springs is still worth getting over an RST Gila.