Do you have a comparable screenshot of your sample San Francisco Terrain - 37.715881, -122.424335

An important note before I explain how to improve texture quality:
For the USA, no any other source has the same quality of souce data as Google.
When all other sources have tiles of maximum 20 zoom levels, Google Maps has up to 23 zoom levels.
The difference is 3 zoom level, means the difference in quality is 8 times.

You have several ways to increase texture quality:
1. Increase the size of the generated texture and / or the number of terrains.
2. Use a custom shader (such as Relief Terrain Pack). This will give you awesome close-range detail, even when the source data doesn't have it.
3. Generate Terrain Layers instead of texture using RWT, third party assets or manually. This can give you a visual quality that easily beat Google Earth / Maps.

Another question please.

How do I improve the quality to zoomed in images?
For example these screenshots are of a point in your sample San Francisco Terrain - 37.715881, -122.424335

My use is to be able to create a Unity game from ground level in parklands.  With as little touch up on the original Maps image as possible.

1) Google Maps for Unity SDK provides a detailed image but cannot zoom into ground level.
2) Google Earth also has a detailed image where you can manually zoom in using the program but no API/SKD for Unity
3) Infinity-Code Real World Terrain - can zoom in but low quality of image

Unfortunately, I did not understand your description of the problem.

If you don't have textures, enable Textures in the Real World Terrain (RWT) window.
If you don't see terrains in the scene view then increase Main Camera / Camera / Clipping Planes / Far.
If you see gray terrains in the scene view, it might be fog. Window / Rendering / Lighting / Environment / Fog - OFF.

If the problem is something else, please explain it in more detail.