Personally, I enjoy buying adventures to "mine" them for ideas. One of the most challenging things for me as both a (non-professional) writer and a DM is thinking up plots and creating realistic villains (I can't emphasise
realistic enough). I buy pre-written adventures--including
Dungeon--to jump-start my creative juices so that I can take the "kernel" of the idea and wrap & blend my own twisted ideas throughout.
Quite frankly, most of the pre-written/published plots I read are fairly crap, and invariably need to be tweaked for the gaming group. I like to add my own unique spin on the plot--I enjoy intrigue, so I enjoy seeing how I can add that element to the adventure. (Things are usually not what they seem in my adventures. I'm sure you DMs understand--

)
(As an aside, I also strongly dislike halflings, flying 'Tinkerbell' fairies, kobolds and other "cutesie" creature NPCs--so I attempt to convert NPC creatures into human equivalents. Demons? Feh. I'm not a fan of them, either--I feel that the human mind can create plots twisted and intricate enough to rival any demon lord (after all, what are we but demons wrapped in a fleshly skin?). Elves--we've perverted them from Tolkien's "beings of light" into tree-hugging humans with pointy ears. Why are dwarves always "gruff" and speak with a really horrible faux-Scottish accent? No thanks. I grew up on Robert E Howard, which featured mostly human opponents. Seems like a LOT of adventures lately seem to feature hafling villages, fairie pranks gone horribly wrong and demons, so I replace them as best I can with human NPCs.)
Anyway, to get back on topic--that's what I use adventures for.
I will continue to purchase them as long as companies print them, then strip 'em down to their bare plot & re-work to my tastes.
Oh, and I like the maps.
