I have the SO/Black M4, and here are a few comments:
1. The interior is far superior to the F30. Now, I did order the full leather, but it really does feel upscale. Far superior to my previous E93 335i as well. If you want your interior to have a very premium feel to it, I would tick the full leather option.
2. I love the SO (and I was deciding between MG and SO as well). Not sure about the resale value hit, but in the end I decided not to take that particular factor into consideration. Another EDer was getting his MG M4 delivered at the same time as mine, and it made me quite glad I went to SO. Not that the MG is bad - it does look good and is quite stealth, but it doesn't bring out the lines of the M4/M3 as much in my opinion, and looks like a regular F3x. IMO the SO is the perfect balance between too loud (AY) and classy (MG). It got a lot of attention/turned heads, but looked classy even in the little understated Swiss towns.
3. I went with the black interior because it provides a good contrast to SO, and I prefer darker cabins. That, and it is easier to keep clean and maintain, unlike the lighter interior colors. Personally, the SO and SS interiors were a bit too bright for me. If they had a darker red or grey option, I may have gone with one of those. But I really do like the black full leather. The contrast stitching looks excellent as well.
I would get you some interior pictures, but my car is currently somewhere in Europe between Nice and Bremerhaven.
