Thank you for actually spelling out what exactly they were complaining about, and I can see how this would be an issue when viewing a monitor. However, you don't have to go to very large distance until the focal distance is effectively infinite.

So I guess the moral of the story then is to combine the 3D technology with a projection system that puts the image at close to infinity (like http://www.mikesflightdeck.com/Scenery_display_2.htm).

I've played around with this lens approach for flight simulators, and I have to say that having the image near optical infinity makes a much larger impression than you might think. You are actually looking through the screen, not at it. The quality isn't great, but it greatly adds to the feeling of immersion. I think this is more important than 3D, since stereoscopic vision really only works at quite short distances.