I take issue with those sections too; you completely ignored that often customers won't know exactly what they want, importance of browsing, and the expert service provided that is the salesperson giving book suggestions and advice to customers.
Your points about alternative revenue streams by providing alternative services are directly covered in 20 year old tv show (black books) where a 'dysfunctional' bookstore either has them already implemented or trials them. For example, coffee is about keeping the customers in the store and browsing, people leave if they get hungry or thirsty. If you're actually deriving substantial profit from your hot drinks, then you're running a niche cafe, and you're in competition against legitimate baristas with fancier machines. It also takes up a large amount of space, and can cause volume issues otherwise.
Most secondhand bookstores are small, and items have a large volume-time footprint i.e. the turnover of any individual item is low. Get rid of all the low margin books for dining, and you ruin the browsing experience in multiple ways. You're just suggesting the secondhand bookstore should ditch it's secondhand books, and instead sell only high turnover popular stuff i.e. compete with modern normal bookstores, which are already doing beyond what you've suggested.
Edit: the parent comment's calcs are wrong too