Last year Valve managed to put together a prize fund for their Dota 2 tournament - The International - by selling copies of the Compendium. It's a digital companion to the tournament, and last year it proved incredibly popular. Valve are expecting the same to happen in 2015.
There's reward systems linked to both investment and participation. As players interact with their Compendium they'll level up and earn a variety of increasingly tempting individual rewards, and as more and more people invest, there's also a selection of community-wide unlocks on offer. These include HUD, Music and Cursor packs, plus an Announcer Pack, a Wyvern Hatching Courier at $9 million, and at the top-end $15 million mark the community will get a new Immortal item and a comic. Head here for more details.