I keep boxed wine in an open cupboard right beside my stove. All I have to do is reach up and get some. VERY convenient. One box has Chardonnay, one Burgundy, and/or Cabernet (right now I have both for some reason). When a dish calls for wine I have it right there and I feel the fact that it keeps for 6-9 months on my shelf is good enough for me to justify using it. I just used the last of my Chardonnay this evening (a friend borrowed for a fish stew) and I decided to taste it - tasted just fine.
No air gets in the bag therefore the taste does not change. I wish they had more of a variety - I'd be inclinded to keep a Sauvignon Blanc on hand also - I think it would pair nicely with the mussels.
We keep some nice bottles of wine around the house and there's no way I'm going to pour 1 1/2 cups of a $50.00 bottle of wine into what I'm cooking
BUT, back to the original question - I think I would use a slightly higher priced Souvignon Blanc - advertise that the mussels are made with such and such of wine - and charge a slightly higher price for the mussels