And so much depends on the size of a property and what habitat the neighbors have.
Other factors include the resources (time, equipment, money) of those endeavored to "improve" the property for deer. Then add "return on investment" to this, before asking at what point is it not worth more of your time & money?
What if "your" property were partially (or fully) owned by other family members or entities, and was likely to be put up for sale (portions or all) within 5 years?
What if you found out neighbors' plans to build a subdivision of houses & mini-farms along one of your property lines?
Every property has a multitude of factors beyond its size and the neighbors
current habitat. One should also consider how things beyond your personal control may be changing in the coming year(s).
As to "return on investment", few habitat improvements will typically yield as much as simply mowing significant areas (annually or once every 2 yrs), spreading lime, and simply broadcasting clovers, annual rye, brassicas, and winter wheat. Of course, you must have areas where the sun hits the ground.