In my opinion, you could have a heated gondola or a 6-pack bubble chair on the Slide Brook line, and it still wouldn't attract many over to Ellen. Again, with most of the seasonal programs and the lodging and the "village" atmosphere of Lincoln Peak base, that's where most people are going to ski. I've had many many excellent weekdays at the MEllen, and then see double/triple the amount of people at Lincoln.
It may seem like Slide Brook never runs, and I've heard that comment from some guests during my years there, but if the conditions aren't right, it won't run, for safety. Not too long ago, SB was only scheduled to run Fri-Sun and holidays. Then it was upped to, IIRC, every day but Tue-Wed. Then, it became daily once again, as long as conditions permit.
Castlerock actually runs quite fast for a fixed-grip. No way could you turn up that lift in its present configuration.... you'd never be able to "bump" it. It's a challenge as it is and requires skilled operators.
Summit was always one of my favorite lifts... probably because it has the nicest on-mountain view, and I remember some warm spring days in April/May. But truly, North Ridge is best for some nice vertical. I believe the trail map back in 90/91 had the ride time of Summit listed as 6.5 minutes.
Welcome back to AZ. We miss you up here.