The expansion offers the following cards:
Not including the Ware cards, the original contains:
As the expansion rules state, the ratio of Ware to other cards should not be altered and in terms of ensuring that the game works this seems to be good advice. These are not altered.
To help each player have a reasonable shot at having at least one of these, keep all them.
To preserve uncertainty when using Animals, keep all of them.
As there are only six of these, add all of them in. Presumably most have played the original game a fair amount already, so let's increase the chances of seeing the new ones. To compensate, remove six of the duplicate Utility cards from the original game. This raises the question of which ones to keep. Those which give players the chance to get wares and especially to get wares from the other player are probably the most important in terms of keeping play competitive.
Although there are more extra Animal cards, the Crocodile is a fairly important card in terms of affecting Utility cards. Thus just add one of each type of these and remove three duplicate Animal cards.
In this set it's difficult to preserve the original ratio between card types. Replacing all of the duplicate People cards from the original with one of each of the new cards still leaves two new types excluded. Thus, remove two duplicates of the original Utility cards as well, altering the ratio slightly but at least including one of every card.
Summary of Additions
Summary of Removals