I was listening to one of my favorite books last night (The eMyth Revisited), I'd recommend it to all vacation rental owners.
It prompted some thoughts. You have created "booking level" and "property level" custom fields. Could you also create "Account Level" and potentially "customer level" fields?
Example: An account level field might be "Website" or "Property Manager Contact Information"
A customer level field might be "Newspaper preference" or "Favorite Wine" or "Family Information". You can imagine the possibilities for CRM (which your system is getting very close to being able to do.
None of the requests are urgent, just wanted to plant some seeds.