Well, for one thing, you get snacks, appetizers and drinks all day in the lounge as well as a continental breakfast. Sometimes, CL means a better location. You also get a lot of personal service from the concierge. We really enjoyed being able to come in from a long day at the parks, grab a few things from the lounge and head back to our rooms and veg out with some goodies. We think it's worth the extra cost with the 40% discount, but I don't know if we'd want to pay the extra at full price, especially if we were doing the DDP as well.
The one time we did CL, it was a free upgrade at the Grand Floridian and we definitely had a good experience with the Concierge. They just seem (for the most part) to go above and beyond for the guests. My daughter was sick with what we thought was a tummy issue and we ordered from the delivery pharmacy. By the time the meds arrived, my daughter was screaming in the bathroom. My DH looked outside and saw the concierge literally running to pick the meds up from the front desk and running back to the bring them to us. We were very impressed.