I've never had problems finding plenty of activities on the mid-size luxury ships. There is always entertainment, lectures, and other activities that you will also find on the larger ships. The nice thing is that you can go to wine tasting or scotch tasting and not worry about the bill. In fact, you and your friends can arrange your own scotch tasting (which we have done).
As for drinks, I probably average a bottle of wine and five or six drinks a day; less if it is a long day in port. There is also no stress about who is going to pick up the tab when you invite new found friends for drinks; there is no tab. I also like hosting a small party in our cabin with drinks, shrimp cocktails, and other snacks without it costing anything.
Also, though a small savings, self service laundry is also free.
I would check out reviews and websites of the various luxury lines. They are all somewhat different.