Whether you spend on board exactly like the op or NOT, I don't believe is the op's point. A lot of companies are doing this nowadays, they assume customers are too lazy or too busy to actually do the math for themselves. Something has no valve if included in a package, that I won't use or buy anyways (internet).
Companies make a fortune on these gimmicks; we don't really drink alcohol and could never justify adding the plus to 'just try new drinks'.
We are die hard 'pay as you go'.... no stress, if we think about every purchase then the total bill at the end of my cruise ...is what it is.