Arc has nothing special at all compared to sh12c.
If you're looking at superiority at photo-taking, Arc does it better, true, but still taking picture on a phone wouldn't get you too far (unless you're talking about p01-c... etc)
Apart from that, what Arc offers, SH12C offers.
Some people suffers from 3D pain and some doesn't, and yes it is gimmicks, but it's stupid to say because it's gimmicks you don't need it. Another function is another function. I'd rather have it, so I can use it anytime, even if I don't most of the time.
Shape-wise, I rate both very high, though I understand SH12C's shape isn't desired by everyone.
Overall, I'd take SH12C over Arc (In fact, I struggled between Arc, Acro, N06-C and SH12C). But do remember the significant shortfall of SH12C against Arc is the camera, and the battery.