For the promotion, EB bumped each of the 4 games to $7.50 each. That comes up to $30, which is 1 cent more than the game costs.
As for the games, I traded in Castlevania Circle of the Moon, Namco Museum, Double Dragon, and Classic NES Metroid. Normally, the trade in value for all four of these games combined would be around $5-$6. Considering that these are games I don't play anymore, and was planning on getting rid of anyways, I think it's worth the trade for Nintendogs.
As for getting that fourth game, I would just go buy a used, cheap GBA games from them and then trade that in. It would still be cheaper than paying $30+ dollars for it.