"To go in for" simply means to enjoy or participate in something. "To get off on" suggests far more heightened sense of enjoyment, almost leading to sexual gratification in some cases. It can also be slightly negative, when someone really enjoys something that's unpleasant for someone else.
I don't really go in for romantic films.
I enjoyed school but I didn't really go in for extra-curricular activities.
My friend really gets off on Brad Pitt films!
Why are you so horrible to me? Do you get off on seeing me get upset?
My boss used to really get off on making us stay late every night.