I wish people who write and study this would differentiate between close languages (eg Italian and Spanish) vs totally different ones (Spanish vs Russian). I am guessing these are cognitively two very different undertakings, in kind, not just difficulty.
Yeah, you probably want to go the farthest distance from where you are currently. A speaker of an analytic language (say, Mandarin) would probably have their mind stretched maximally if they went for something agglutinative(say, Turkish) and vice versa. Geographic and cultural distance makes this even more of a mind expander.
