Well, I’m on this One Page Campaign kick right now, so I’m just going to roll with it a bit. Actually, thinking on it more, it’s probably more accurate to call it a One Page Hex Crawl, because that’s what it would turn out to be. As the party explores they have roughly a 1-in-6 chance of encountering as they forge through a hex. Not every encounter has to be a one page dungeon. Some might just be weird monuments, abandoned ruins, random monsters or some such.
While you’d have to pre-place any dungeons you seed as treasure maps or important points-of-interest, you wouldn’t have to prep every single hex beforehand. If an encounter happens, you could just make a quick roll on some charts to determine what the encounter is (for example: 1 = dungeon or monster lair, 2 = ruins or monument, 3-5 = wandering monster, 6 = special encounter). If a dungeon, lair or other structure is rolled, it’s set in that hex for the rest of the campaign (though monsters could reoccupy a previously cleared dungeon). One of the great things about using one page dungeons is that you could just print out a bunch you like beforehand and then randomly draw one when needed. Determine its level, either randomly (roll 1d10 for dungeon level) if you want to be hardcore, or use something like every hex out from a large settlement increases a dungeon/lair’s difficulty by 1 level, if you want to give the PCs a chance ;). Then make a note on the sheet of it’s level and hex number.
If I have time I might work up an old-schoolish one-page supplement for hex crawling and wilderness encounters. Cheers.