Water feature.
As long as it is well kept and has fish and non-nuisance wildlife (no mosquitoes), and hard pack sites with grass so RVs don't sink, people pay a premium for "water front property"
Proper drainage and be smart with your wind direction for dumpsters and sewage treatment area, etc.
Ruts, muddy sites, unlevel sites are turnoffs.
I've seen nice bath/shower houses that look almost prefab with splitface stone, concrete floors with natural drainage, solar heat with gas instant heat backup.
Edged walking paths with subtle LED lighting at night, benches for great view enjoyment, field areas for group games, play area for kids (think swings and slides), bike and walking (exercise) trails.
Parks with nice concessions, camp stores, and game rooms (maybe) seem to be packed all the time.
Be aware of firepit placements that don't interfere with awnings or funnel into the next camper's bedroom windows.
Separate area for long term camping (think "villages") with their own facilities and laundry
Plan some areas for really big rigs with adequate turning radius.
"Loops" seem to work well with facilities, playground, green areas, and such in the middle.
Trees. People love trees between sites. Try to avoid anything messy, like pine sap and pine cones, etc.
Hope some of this is helpful. ;)
