I've made a couple trips up the road to play those two courses and regarding the beginners and so forth, yes I think Mid-Pines is "easier" in that it plays a good bit shorter and the greens on balance are a little less tricky. Just about every green at Pine Needles seems to have one or more sides on which a subtle roll-off can cause you problems with what you think is a well-placed approach. More of the greens at Mid-Pines are "what you see is what you get", plainer.
Pine Needles always seems to drain better. During dry weather I think Mid-Pines plays fast and just a bit scruffy in that manner appreciated by a lot of people on this forum. But if it has been wet or it's in the winter, I've made at least one trip where Mid-Pines seems a bit muddy in comparison to the more prototypically "Pinehurst" conditions across the street.
I substantially prefer Pine Needles and for my part Mid-Pines is a nice warmup and/or change-of-pace in comparison. If I were going to be there for multiple days I would certainly play both but if I had a single round or even a single 36-hole day it would be at Pine Needles, no question. I've never visited during peak season and so I've not experience the kind of backups you mention. On an empty course you could go around Mid-Pines in 2-1/2 hours and probably shoot under your handicap if you chip and putt pretty good. Pine Needles even one day when I played it dead empty seemed to take my threesome well over 3 hours and that's partly because we seemed to face more tricky/touchy shots around the green and found more bunkers.
I think for the kind of course it is, Mid-Pines is wonderful. If I made a trip and were forced to play just there for several rounds I would not complain (absent any 5-hour rounds of course). But to me Pine Needles is an all-world quality course that I'd as soon play as most anywhere in USA. A number of Dixie Cup participants from a few years back differed.
Sums up my opinion almost exactly. They really are two great, but different experiences. Its very apparent to me that Mid Pines is a bit more scruffy, scraggly, and at times colorful course. The shorter yardage, the winding routing, it definitely gives the "back in time", or even cozy feel. Its the easier of the two, yet no less interesting. MP's got some amazing charm and beauty, but gives me some memories of some muni I can play any weekend at the same time.
The vibe at Pine Needles is "championship" as soon as you step out of the clubhouse. Bigger and more streamlined, you need both more power and finesse compared to MP. The winding routing gives you a more isolated, you vs. the hole feeling.
I think its fantastic that there's two significantly different courses about a 6 iron away from each other. Love em!
Here you can see a bit of the rough edges of Mid Pines (in the fw of hole 5), then compare it to the clean contours of the 1st green at Pine Needles.