It could easily be argued that one reason for the popularity of Planet Comics is that many of the covers are so good, they're all classics. Maybe not all, but many. (The only problem I have with designating #65-70 as classics is that except for the astonishing covers, the interiors were all reprints; so yes, the covers are classics, but the books as a whole don't complete me ).
Another way to define "classic" would be to include the books with covers (or interior art) by key artists: Eisner, Fine, Fletcher Hanks, Renee, Baker, Ingels, others. And of all the stories, I think Mysta of the Moon and Futura were among the better drawn and better written GGA stories, so I'd give a nod to their first appearances (#35 and #43) as classics.
In addition to the ones you listed (#2, 5, 8, 17, 18, 19, 33, 35, 45, 58, 59, 65, 66, 70, & 72), I would say that #10, 11, 12, 14, 24, 28, 36, 39, 44, 48, 52, 55, and 56 make me drool. And that's just when I'm taking my anti-drool medication!