the best practice would be in the type you are flying on a daily basis, not the use of dedicated gliders.
as to sully, I understand he took gliding lessons early in his flying career. that's nice. but the basic skills of airmanship are practiced every day in routine flying. they are called the four fundamentals of flight. and while he didn't shut down engines (to get rid of residual thrust) on a routine basis, i think the argument for flying gliders to help you fly airliners is pretty far fetched.
Unfortunately, we get WAY too little practice on a daily basis on the "basic skills of airmanship" in airplanes with autopilots, autothrottles, and FMS; and in a regulatory environment that forces us to couple up for 90% or more of each flight.
While I might agree that there is not a need for "dedicated" gliders or glider training for airline pilots, I am an advocate of encouraging EVERY pilot to get some training and time in gliders. Glider time is virtually 100% "basic skills of airmanship" time, and I still believe that I learned more about flying, per time spent, in gliders than any other aircraft. Some of those skills are not easily forgotten, and may come back at the most opportune times...