Wow, $39 is a lot for a mag sub? I pay a lot more for The Economist, though that is admittedly a weekly mag.
I get both Dragon and Dungeon. Both are entertaining. Dragon has more player-oriented content and better comics (Nodwick, Dork Tower, Order of the Stick, Zogonia). Dungeon is mostly adventures and DM-related content.
I find the general quality of both to be high. Paizo regularly puts out slicker content than many D20 publishers. Generally, the content of both is worth reading, even if you don't use them in a game.