Going by Amazon.com, ME2 will get you $40 from a trade in copy.
ME2 has what is called the Cerberus Network, which access is given free to new game purchasers and is $15 for those who get it second hand.
So far the network gives access to two mission, a character(whose position on the party select screen will be empty for those without access to Cerberus Network), armor, and weapons. There are 5 new missions and a new vehicle being released for the CN in March.
They sale new copies of the game for $49.99 (as low as $47, if getting from an individual seller). Used copies can be purchased starting at $45.
It doesn't seem like the resale value of this game was hurt by this method of DLC. Are we creating situations in this thread that do not exist?
The more I think about it, resale value is hurt more by a glut of used copies hitting store shelves. Getting free DLC trickled out to you over the course of months means people are more likely to hold onto their copy, thus keeping the used sale price inflated.