Agree, this would be useful. The longer the game has been out the more competent many players have become with the terrain tools, so it's probably time that some advancement was made on them. A lot more people seem to be using them now than before (including myself).
I'd also like to see a 'stamp' function applied to the terrain paints. It would be much easier to paint habitats with a square-edged stamp and to avoid the terrain leaking out into other habitats or the zoo in general. As an example I wanted to contain some snow in an indoor section of my snow leopard habitat but due to the big round brushes it was next to impossible to keep it from spreading beneath the walls, which made it look really ugly (especially when the sun was shining outside, since it just looked stupid to have frozen snow sitting there in a 26 degree day).