If you don't have much grass ( heh, and a fast computer ) you could always try to use the paint effects tool. Otherwise, you could try and experiment with duplicating your grass plane you have now, put it a little higher in the y-direction and applying a darker, transparant texture, witch bumps a little more random below to make the grass looks 'thick'. However, I think you would have to change the settings per viewpoint, because it ain't grass and it will never be . But it's a good supstitute and besides, if you reall want real grass you will have to model every single poll, and you will have to do that billions of times .
About the building, if you do not make it reflective, try adding some small attributes like scratches or add some dirt. I'm not really the texture kind-guy, so I can only give you creative suggestions . If you think you have the right texture already, try putting it in front of different colours of light to see how it reacts. This doesn't change anything until your final render, when you have set the sky and such, but since you start texturing the things you make at start, you might want to check that too .