Emerald Dream PServer before Nost only had 900-1500 on I think and it was fine, don't need to have 10 000 constantly online like during Nost peak. Early/Mid Nost was perfect at like 5k uptime 2k downtime, and even 5k is a bit much.
Edit: also, even with a large population like on Nost of course you have more server identity than retail, but Nost compared to ED server was much more anonymous; leaving dungeons/ninja-ing/being a douche wasn't as bad a mark on you because the server had so much people on it and lots more people coming and going. In a way, although ED was more broken and had less pop, people there were way more dedicated than Nost. It might have taken you longer to find group for a dungeon but once you had one no one would leave.