While my wife is a niddah, may I gaze at her body when shes dressed tznius, but the pleasure I get is sexual i.e. is her covered body considered like her face?
It is permitted for a husband to gaze at parts of his wife when she is covered even though he has pleasure from looking at her. However it would not be permitted if he knows that it will cause him to have improper thoughts.
Rema Y:D 195-7, Shach ibid 12, Shevet Halevi ibid 3, Halchos of Niddah pg. 134.