I own this collection http://www.doschdesign.com/products/vizimages/Birds_Eye_Trees.html. I use it from time to time with photoshop.
For me, I wouldn't mind a few more top view options. I include a plan view with all the designs I present to clients. Most of the time I do them in a program called Dynascape and the plants are represented as symbols which are more CAD then they are photoreal. I need this so I can do callouts which label all the plants in the design. This allows my installers to accurately place and plant the landscape.
What I would love to see would be a way to "hook" a top view plant to a normal faceme billboard in sketchup so when drop in a tree, the overhead view comes in with it....perhaps on it's own layer. This way when the camera is overhead, you'd get a nice depiction of the layout in a photoreal sense. When you use faceme plants, if you switch to a top view and turn off shadows and perspective, the plants disappear. In the past, when I've used sketchup to do a layout presentation for a landscape design, I would import from my library of colored CAD symbols and place them where the plants will go and put them on their own layer. Then I'll bring in all the faceme plants and put them on top of the symbols. I shut the symbol layer off for different 3D views, then I'll turn them on for an over head shot. Works good, but it's a PITA.