Doing Volks Auto contracts will give you a set of arms and legs, doing Luxen will give you unique panties (Not sure if there is an unique bra too), there is secret parts in the ladyparts store, got the rainbow hair, but not sure what other secret parts could be buy, maybe a new personality or tail.
So good lucks there, it takes time to get the VolksAuto parts and also the unique panties from Luxen, so be patient doing the contracts.