Totally confusing isn't it?
I've never used the /nogui comand because it throws off the simple installation flow, and because I've never had to use it before. Every GOG game I've installed worked fine with gdiplus and practically any version of Wine. This is why I'm surprised you are having so many problems with the Sacred 2 installer.
Daerandin from GamersOnLinux uses the /nogui all the time which proves that it "can" work.
I just wish PlayOnLinux had a way to add commands during a manual installation, then we could easily just add /nogui for GOG installers.
I'm glad you got Sacred 2 installed. If your computer is fast enough, it should run nicely. I would get random crashing, but I have a feeling that problem is resolved with newer versions of Wine or the "staging" versions.