Marketing adventure-aids to players won't work, I don't think. You already have an issue with adventures themselves that only a small fraction of the GMs who buy game products will want to buy an adventure (let's say 1/10). If we figure a similar fraction (1/10) of players would be interested in adventure-aids, we have to multiply the two fractions. Only 1 in 10 players are playing that adventure, and only 1 in 10 of those players will buy the aid, so now you're only marketing to 1 in 100 of your potential players.
Of course, those numbers came out of my rear pants pocket, but you can see the point I'm trying to make.
If I'm reading things right, the biggest money-makers WotC has right now are their collectible games -- Magic, D&D minis, Star Wars minis, and other various card games. What they could try to up the sales of adventures would be to bundle adventures in with existing collectible items.
F'rinstance, imagine there was a collectible D&D starter set. You buy it for $25, and you get the basic game rules, the rules of the D&D minis game, a random adventure, and 20 minis that fit that adventure. Every year WotC could put out a new series of linked adventures, and have the mini sets that come out be maybe 30% filled with minis intended for the adventure series.
Say they start off with GDQ. The starter set has a short 'defend the town against some giants' adventure, with a few giant minis, and minis for the various pre-statted PCs, and for various henchmen of the giants (because, sadly, you can't make a mini set that only has giants; you've got to have some variety).
Then there'd be three expansions in August, January, and April. Giants would be released in August at Gen Con, and would have 30% of its minis made up of things the party could run into during the Giants series of adventures, and each mini box would have a small folded up booklet with a scenario that fits into the Giants adventure. In September they'd release a Giants boxed set, which contains everything you need for the adventure, including minis and maps.
Now normally you couldn't do this for just any old adventure -- economies of scale would make it unfeasible to create minis that would only be used by 10% of your customers -- but since you're already making the minis anyway to fit into the miniature game, you don't have to pay folks to design new minis or set up the mini-mint or whatever it is to pump out new items. You just make sure that the minis you're making can serve double purposes.
In January you'd release the Depths of the Earth expansion with affiliated adventures, and in February you'd put out the complete Depths of the Earth boxed set. In April you'd release the Vault of the Drow expansion, and in May you'd put out the complete Vault of the Drow boxed set.
Like Magic, you'd have a new cycle every year, to keep things fresh. Players of the D&D minis game would just pick up packs of minis for their warbands, but the inclusion of interconnected scenarios might get them curious about what the big adventure is. People who buy the pre-packaged adventure would also be exposed to the rules for the minis game, and they'd have an incentive to buy the minis boxes if they wanted to add to their campaign.
Does that sound like a valid market strategy?