Air Shock Question

So I'm looking at eventually doing all the chassis/suspension goodies for my valiant. I've been fabricating for a long time and have done a lot of motorcycle work. So, I'm interested in taking the routes that cost more time and effort than money, where I can. I'll be fabricating the rear suspension and find the instant adjustability of an air system appealing... but not at the cost of performance. Also, not gonna drag it. Might get it on a road course but not building it just for that. Do the performance characteristics of springs outweigh the convenience of bags?