[Pål Jensen]

Just to satisfy my own curiosity, I took a couple pictures on my K-5 , that would be equivalent on a D800. The 35 and 50, 1.8, same tripod mount. On a K-5 and a D800 that should get you approx. the same FoV and the same pixel count. DoF on the 35 2.4 wide open was 12 mm, again approx. On the 50 1.7 is was 6 mm. SO yes, narrower depth of field. But not without complications, the 35 image was by far the better image, and because the 35 focuses closer, I couldn't even take the original set up with the 50. That's the problem, the theory is great, but real world, you just never know what you might run into. You might just get the picture you want on your APS-c and have to use the 35 and crop it to APS-c size on your D800, which would negate any advantage.

FF might be an advantage, and it might not. Depends on the circumstances.

Yes. One of the advantages (among too many to mention!) with APS is shorter focusing distance at the same magnification. This, in addition to the extra DOF, means you can shoot these near/far landscape images before only possible with large format (due to their tilt/shift possibilities).

The idea that narrow DOF and wide angle is something that has not been utilized to its potential due to the lack of fast wide lenses is missing the mark too. The truth is that such possibilities have existed for a century or more for MF cameras (and larger). The 28mm (35mm system or FF) equivalent in angle of view for the 645 system is a 45mm lens; theres no problem isoltating the subject with this lens at 2.8, Not to mention the 6X7 system where the 28mm equivalent is a 75mm lens.
But for some reason wide angle images with no DOF has never caught on. The reason is simple; you use limited DOF to exclude something but wide angles to include things. This doesn't not go well together (although exceptions exists).