Indeed -- "Best" quality is the only way to get every drop of graphical detail out of the export process. Even the next quality down will reduce the texture quality of high-resolution textures or close-up shots (see my Scrolling Credits Demo for an example of this). Going down even lower will force the game to use less detailed sets, and may even remove components from your shots.
So as others have suggested: play the game on a lower setting, but always switch to "Best" before export.
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June 8, 2008 : Sci-Fi Bridges, Danger Dojo, plus new version of Mesh Reconstruction Utilities