I'm 80% a DM (over 20 years now) and 20% a player; gaming on average about 1.25 times per week. Having said that, Dungeon is worth its weight in gold to me. I've been a subscriber for years, and get value from every issue. I rarely, if ever, run the modules "as is". I have my own home-brew world, hence the modules always need some massaging to fit. But having the basics available is such a huge time-saver, I can't imagine running a regular game without it.
Dragon is more hit-and-miss. Overall, I think the quality is higher now than any time in the past, but it's still something I only buy about a third of the time (maybe 4 issues per year). Given my homebrew, I don't get as much value from campaign-specific articles. Faiths of Greyhawk... Cities of the Realms... Lands of Eberron... these things are all pretty much wasted on me.
However, those issues that are more general are *really* good. My personal favorites: the Demonicon of Iggwilv, Creature Catalogue, Class Acts (new format), OOTS and Zogonia, and one-off gems like...
#336: Haunted locations
#337: Illithid-related creatures
#339: Planescape faction items and prestige classes
#341: Variant golems
#345 (perhaps my favorite recent issue): Artifact spells, giant magic items, sea serpents, unusual transports (and of course, the Demonicon and Class Acts)
I didn't buy 342-344, nor did I buy 346... but I can always count on the fact that at least a couple of the next 6 issues will rock my world.