Ben,
Have you set enhanced rendering for text and lines, as well as for
rasters? It's something I always set as it really seemed to make a
difference to the output (print or as an image). There is another option (PrintOSBM) hidden away in the registry that you might need to set when printing with
translucent layers. Have a look in the MapInfo Printing Guide v10 page 18
as it describes the option and how to enable it –