It's worth it if you want the adjustability and tuneability. I have 14" King coilovers and I love the ability to fine tune my ride height down to the milimeter. Dual rate springs that are easily changable is nice too. They are also the last shock you'll ever need to buy. King will rebuild them for $50
The bad: They are noisy, the slider that sits between the springs bangs as it loads and unloads. (I think there's a fancy slider that alleviates this but I don't have em) Annnnnnnnd They are freaking expensive.