I find Pre-Orders bonuses only really relate to the retailer GAME. For example, if you pre-order Yoshi's New Island from the you get a Yoshi Egg Carry case. You end up putting £5 down, but that's taken off the cost of the game at retail. Problem is that the games are more epensive from retailers than compared to amazon where I get most my games, so the pre-order bonus is just an incentive to pick it up from the store.

If there is no extra goody for pre-ordering though, don't do it. I just wait for the game to go down in price unless I want it Day 1, or are interested in the sucess of that series (e.g. fire emblem, bought that day one beacuse we don't see many strategy RPG games on the 3DS and it'd be cool to get more hint hint square enix.)