I created these renderings in Photoshop based on views exported from Sketchup. I'd love to get feedback or ideas on how to make the graphics more compelling.
I was always way too busy during my LA design career to learn autoCAD or Sketch-Up.....I have always been comfortable with "hand drawn" color renderings/graphics. So, I'm probably not the best person to critique your work.
I would recommend that you GOOGLE........"Sketch Up renderings". You will see many fantastic samples. These samples will give you an idea where you....and what the Pros are producing.
As you are presenting what appears to be a public space I would add more people: make the space alive.
And while I am not a SkethUp artist, it looks flat to me. The structures pop but the landscape is indistinct. That may reflect your design priorities and what you feel it is important to communicate, but for me they do not feel compelling landscapes.
This is a good base. As Mark said, combining real elements with sketchy ones throws off the focal point of a rendering. My eye goes to leather jacket and the flags and wants to know why they don't belong. If you're going for non realistic try Filter>Artistic>Watercolor or Sponge or something to take the bluntness off a real object. You will then want to blend the elements. http://www.sketchupartists.org/tutorials/sketchup-and-photoshop/ is a great resource.
If you want photorealistic download Podium for Sketchup and render the scenes before bringing them into Photoshop. I imagine you guys touched on that in school. Podium isn't the best rendering engine but its learning curve is not steep compared to V-Ray or trying to learn 3D Max for top of the line photorealistic renderings.