I agree, a new post, and leave the old post intact, but edit it to include a big "This list is outdated, see Fancy New Post" at the top.
I agree with this. You don't want to delete or majorly modify a post that has a lot of comments and discussion. It's better to just move them and put a note at the top and possibly in the title (like an [outdated] tag).
The changes you make should be major enough to warrant new posts, as half the cards in cornucopia need to be at least considered for the "best" lists (hamlet, menagerie, remake, tournament, young witch, and hunting party). Though it does seem like it might be a waste to make a new post about the $5 attacks for instance, since there is only 1 new $5 attack, and it probably doesn't belong in the top 5.