More importantly b) the whole point of Daleks is that they're genocidal psychopaths. They have no interest in enslaving or incorporating other races, they want to eliminate them. They are the Nazis of the Who universe, convinced of their own superiority above all other species. In that regard, neither their assimilation of Oswin nor their use of the puppets made much sense./QUOTE]
There is a "history" of Daleks using and "assimilating" other species.
In the 1st Doctor episode, The Dalek Invasion of Earth, the Daleks have enslaved humans to do heavy labor and mining.
In the 3rd Doctor episode, Day of the Daleks, the Daleks employ mercenaries called Ogrons.
In the 6th Doctor episode, Revelation of the Daleks, they use human corpses to create more Daleks.
In the 7th Doctor episode, Remembrance of the Daleks, one faction of the Daleks uses a human child to boost their combat computer.
In the 9th Doctor episode, The Parting of Ways, that faction of Daleks have been siphoning human beings to cull genetic material to make more Daleks.
I think Dalek motivations have changed to suit each episode.