Many people in this thread seem interested in the "encounter in a box" idea. I've been thinking more about this over the past day or so, and there's another way you could make this even cooler, so cool I'd be excited to buy it. Thrilled even.
With the encounter-in-a-box, also include a sheet or two of unique dungeon tiles that are exclusive to the product.
For the drow-themed encounter-in-a-box, you could have one big tile of a shrine of Lolth, then another sheet of tiles for terrain features like spider-shaped braziers, idols, spiderwebs, bodies wrapped in webs, a cluster of spider egg sacs, et cetera.
There are many themed sets you could throw together with this idea. If you made these mostly with reissues of older sculpts (sorta like the way the Player's Handbook Heroes is set up), I'd still buy it because I never can have too many kobolds/spiders/whatever. Even if it only included two new sculpts (or even one really good one), I'd still be thrilled.
Here are some of the encounter-based packages I've been fantasizing about:
Kobold Encounter in a Box (Target levels 1-3)
• Six Kobold Soldiers (Angelfire 44/60)
• Kobold Wyrmpriest (Dangerous Delves)
• Two Kobold Champions (Aberrations 37/60)
• Two Kobold Trapmakers (Night Below 35/60)
• New mini: New or awesome rescupt of a medium chromatic dragon of some sort, statted out as an elite like in Draconomicon.
• New tiles: Kobold dragon shrine/lair, trapped treasure chest (closed on one side, opened with trap sprung on the other), portcullis trap with draconic look, dragon altar, braziers, pit trap, arrow trap, a few different trapped doors.
Undead Encounter in a Box (Target levels 4-7)
• Six Warrior Skeletons (Archfiends 43/60)
• Deathpriest of Orcus (Against the Giants 3/60)
• Two Shadows (Night Below 60/60)
• Two Ravenous Ghouls (Desert of Desolation 54/60)
• New mini: Some cool new undead that we've never seen a mini of before, such as a brain in a jar, a deathkiss beholder, or an undead angel.
• New tiles: Crypt, sarcophagi, caskets, pillars, funerary altars, open graves, gravedigging tools (shovels, lanterns), necromantic circle, gruesome necromantic work area (surgical tools, blood and guts, that sort of thing), enbalming table.
Infernal Temple Encounter in a Box (Target levels 8-10)
• Six Legion Devil Legionnaires (Savage Encounters #24)
• Tiefling Cleric of Asmodeus (Demonweb 8/60)
• Two Tiefling Warlocks (Dungeons of Dread 47/60)
• Two Succubi (Blood War 59/60)
• New mini: Aspect of Asmodeus, or another archdevil of some sort. If they made an Aspect of Bel, it could also double as a Pit Fiend for higher-level groups.
• New tiles: Infernal temple, sacrifical altar, devil statues, manacles, prison cells, candelabras with creepy shadows, cozy divans and seating, desk with infernal contracts, ritual circle, ritual work area with creepy infernal trappings, "gate to hell" teleportation circle, flames, burning objects of different types.