I have air bags on my 67 and I love them. total cost was about $1k and I did it myself, not that hard to do. Kit consists of 8 valves from ez air ride, 2 5g tanks, 2 compressors, 4 air bags from Universal, 1/2" lines, mounting brackets and shock relocates for the front, 2 dual gauges. All of this was mounted on stock control arms (new bushings and balljoints) with no cutting involved. I can have it back to stock in a day.
I've tried different springs including 2" lowering springs ($500 from Eaton) and it was still too soft, felt like a boat on the freeway. Now with bags I set the front to about 100psi and back to 50-60 and it rides smooth but nice and firm. Not as firm as my Chevelle on coil overs but not as soft like it was on springs, IMO it's just right. Ride quality and cornering is dramatically improved as the bags reduced the body roll. Freeway driving is amazing now as it doesn't bounce around, but yet it's still very comfortable.
You don't need to spend $6k to have a quality (simple) air ride.