Optimizing: Dealing with the background


I am making a side-scroller and I built my levels with some illusion of depth using other 3D Meshes in the background and finally using the skydome as a back drop.
I was wondering if there was a more optimal way to avoid using 3D Meshes and to have a simple flat texture instead or to crop the 3D textures to save space and loading times/performance.

Here is a snapshot.

Anyways, anyone have any experience with this?