The text speaks for itself here - You can cast Dragon spells without paying their mana cost
Having that extra bit of speed for every single deck type in the game can be surprisingly powerful, as it can essentially put the player one turn ahead of their opponent in terms of resources
In practice, it means an opposing Blasphemous Act will only deal five damage to your board, and a Chandras Ignition will deal double damage to everything that isnt yours (and incidentally, only half to your creatures)
Unlike today, when each player can have a copy of a legend on the battlefield, in 2000, only one copy of a legend could exist on the battlefield, period, between both players
This adds a minimum secondary market value of about $12 to the bundle, but theres a good chance that secondary market values for these variants might work out to more than that