As long as the AI file is all vectors, there is no quality adjustment - as opposed to rasters and there dpi and/or compression settings.
Saving as AI is easiest and most editable, but you can also save as eps or press quality pdf if you want. If you do have any raster components in teh AI doc, make sure they're at least 300 dpi (600-1200 if there's text in the raster).
Using OSX 10.3.9 on a G4