Errr.... Timeout here people and let's look at simple dollars and cents...
Using ODST to trade-in, you're 'buying' it for $68 and getting ~$97 credit at EB...
Now I'm pretty certain that you'll be able to get 3 trade bait games for far far less than $68 (~$23 a game!) and get $99 credit a JB for exchanging the copy of Batman you got with the 3-for-1 deal....
At the moment you can walk into any EB, without really hunting, for trade bait and pickup three $20 games for $60, $54 with EDGE...

No?