(1) This never bothered me, but I suppose there should be an optional which can enable/disable this feature.

(2) Such is an effect that is really only supported by intense hardware, which many users of 3DGS simply don't have. Essentially the lighting effects would have to be calculated in realtime, which would have a terrible effect on one's processor. That and none of the surfaces in the level would be optimized or culled, and that would hurt the performance a lot. Thus, while such a feature would be useful, it's too demanding of one's rig to be very effective. :\

(3) I think you're right on this one. There could be a preview button in the sound's dialog box that enables you to hear what the sound would be like in game, from the 3D view's current position.

(4) Yes, yes, and yes. Manipulation of textures could be much better.

Of course, since I'm mostly just a programmer I don't look into many of the details of these editors, so a lot of it doesn't bother me. But like I said before, a serious user might need something better.