Hi guys,
Just signed up so I can post the progress I've made with this bug. Thanks to the above posters for help narrowing it down ^
I seem to have "fixed" mine now. What I did:
Went to Windows/Fonts folder, and copied the BankGthd.ttf and Consola.ttf files, then pasted a copy into: GalCiv3 main directory, GalCiv3 Fonts directory, and to the My Games/GalCiv3 directory.
I can't tell you which file fixed it, or where I put it.. but now I appear to be able to open the game multiple times without having to reinstall, saving me huge time/effort.
I can't promise everyone's issues will be fixed doing what I did, just relaying the info in case it helps others.
My problem appears to have been some sort of permissions issue in accessing the font files... putting copies elsewhere in the game directory seems to allow it to use those instead. Win 
Hope it helps someone!
Cheers