This is all great advice, thank you. In fact, I did, instinctually, put my neo socks under my bag and they were dry and warm by morning. I guess what I did wrong, in the end, was keep wearing them once I'd stopped. I was on Horseshoe Mesa in freezing temperatures, and the sweat inside the sock began to freeze—I was too focused on getting some food, and getting myself into my bag that I didn't take the time to change into my sleep socks. Then again, I really didn't want to get them wet. I just kept thinking, as ice started caking everything, that any minute now I'll be tucked up in my bag—conditions were wet and very muddy too.
So, the lesson learned is definitely that if neo socks are to be used it has to be in sub-freezing temps. Then, once stopped, they need to be swiftly swapped out (the plastic bag/sleep sock solution suddenly seems like a no-brainer).
For persistently wet conditions, in the future I'll have a pair of sealskinz at the ready for above freezing hiking.
Thank you all for your 2 cents on this matter.