You need to be both consistently drinking quite a bit to get value out of $75 per person per day. Assuming a beer is around $7 that would mean 10 pints of beer plus a couple of speciality coffees every single day in order for it to be better value than just purchasing as you go.
If you are a wine, spirits or cocktail drinker then it may pay for itself sooner, but even so, you are going to be drinking many drinks every day in order to make it pay.
I think for Queen's Grill it would be even harder to derive value, as you get free alcohol provided in your suite anyway, as well as a full bottle of champagne upon boarding.
So bottom line is, how hard do you like to party? 😀