Barbra imported trees and large plants from all parts of the world. She lived at the end of a road in Malibu with much more modest houses in front.
Yes, Barbra had concerts there for charities, and anyone who bought her property would have made major changes also.
With all her building and renovations plus the trees and plants, she was not popular with her neighbor. Worse, Streisand did not set aside any money for the upkeep of the property. They had to open it the public with admission fees.