Here’s an article specifically talking about the value of curb appeal, from a dollars and cents perspective.  It even breaks it down to what trees and fencing are worth. Most landscaping (as with any home project) should be done for your own enjoyment, but it does add to the value of your home, either in the form of a faster sale or in the form of a higher sales price when you decide to sell.   Some experts believe that mature landscaping can add up to 25% to the value of your home.  If you have been thinking of sprucing up your exterior- have a look at this link!  It may give you some good ideas of where to invest your money.
http://www.houselogic.com/home-advice/landscaping-gardening/landscaping-home-value/