You get 10% discount for purchasing any drinks package online prior to the cruise. You then get your loyalty discount off the pre purchase price as well. So Baltic tier for instance would get 10% then a further 10% off the discounted price, so 19% total. Not 20% like one of the previous posters thinks. If you want to be really pernickety the rounding down to 2 decimal places is done after the number of days is multiplied by the discounted price per day so there is only one rounding down done.
Re the OPs reasoning. If each kid had 4 soft drinks and each adult had 3 nice glasses of wine, a cocktail and a coffee thats break even point.
I'd go for that personally thats not a bad proposition. YMMV