I quite like the idea of pre-order and new game bonuses that don't actually affect the game in any way. So if someone bought my game new, I'd include something like fun costumes, game modes that alter physiology (think, big-head mode, but not necessarily 'big' or 'head' related) or visual-filters (like, 'Optimistic', where everything is either shades of yellow and white or are other colours, but brighter tones), you know just stuff that doesn't affect the gameplay at all, it is just a little optional thank you for people buying new. And for pre-orders, throw in a collectible of a well-known game figure (like a plushie companion cube with Portal 2, or a keyblade key-chain with KH3 ... you know, just little doo-hickeys).
So you know, give people a full game on disc, but have completely optional extras, that in no way affect gameplay for those who pre-order or buy new copies. Also, if the game warrants it, throw in an expansion pack a year down the line (about $30-40, but with about an extra 20-30% gameplay).