The VDH is the best (or one of the best) optical cable out there ($150). But pairing with the DS5100 using its wireless phone, it sounds bloomy & muddy (But this is not the case when using a plugged phone). I suggest the Oehlbach, costs less than $50 & IMHO it is a good match with the DS5100.
Check audioreview.com for a slew of TOSLINK cables. There some rave reviews for the harmonic technology silver platinum opticable which was said to creat a BIGGER SOUND IMAGE and DEEPER BASE on receivers that didn't with other cables. It looks as if sony made a boo-boo with supplying their own cheap cable in the first place!
You are right, the only place a an optical cable would be better than a coax would be in a magnetically noisy environment. The only way I see that an optical cable could sound better than another would be the quality of the fiber or the connectors and my guess is the connectors. As far as signal degredation the cable is so short that it won't matter, unless it is bent too far.
Personally I would pick a digital coax over an optical any day because there is one less signal conversion you have to worry about. For example, if you use optical cable for your CD player here is the path of the signal:
Digital (elec.) -> Digital (optical) Trans ||| Digital (optical) Rec -> Digital (elec.) -> analog
||| Represents the cable
I say order one where you have a demo period if you can't tell a difference from your Radio Shack special you don't need to uprgrade. However, I have heard good things about Van den Hul cables but I have no experience. Plan on ordering some soon though.