Samurai Trilogy is really cool – a great narrative arc, beautifully photographed (in color), and obviously boasting a great performance by the inimitable Toshiro Mifune – though I wouldn't necessarily say it has the same sort of ethical and philosophical heft of Kurosawa's samurai films, for instance.
I'd also strongly recommend The Leopard, amongst the films on your wish-list: Burt Lancaster is great, it narrates a really interesting period of Italian history, you get two different cuts of the film (one a solid English-dub, one longer-cut in Italian, which I prefer), and the cinematography is incredibly lush — plus Claudia Cardinale.
As for the digipaks: I've generally prioritized the sets when purchasing, since usually it's a better film-per-dollar ratio and moreover because I really like studying and getting to know specific directors and/or periods. I also generally tend to buy more Criterions that I haven't seen before — hence why I haven't jumped on On the Waterfront, which like you say looks magnificent, or Videodrome, which is another of my favorite titles.