Well originally, I was getting a lot of flickering on the main character. I read that sometimes ATI cards had issues with GK3. One solution was to run in software mode. I posted a message here about it. Basically, I turned off "Incremental Rendering". That allowed me to run in hardware mode without the flickering. It was a bit slower but worked. Unfortunately, running in hardware mode was causing the pop-up text to become blanked out. Even the text entry for saved games was invisible. I decided to accept this and continue play in hardware mode.
As time went on, I kept updating the ATI drivers as they were released and eventually I looked up the "LOD" option. Facepalming myself for my silly oversight, I upped the level of detail slider and improved the graphical quality. I believe that it was around this time that the text returned, but I cannot recall if it was before or after this change.
The only modification that I have applied to the game is forcing the resolution to 1920x1080. I have been using this since I began playing, both during the flickering issues, the invisible text and afterwards.
You might try contacting "The Collector". He hangs out here and at The Sierra Help Pages. He's usually quite knowledgeable about these sort of things.