It seems very primal and personal. I don't think it's new agey bullshit because it seems to have very old roots into tribal and shamanic practices.
Anyway now that made me think that in all my life I used to be very strongly attracted to wolves, but since recently I started loving snakes and being attracted to them instead. I guess my "totem animal" changed (I prefer the name "totem animal", it resonates more with me then "spirit animal").
Now what are the concrete applications, probably no real concrete application because it's so primal and linked to instincts, I think it does have meanings in the deep psyche but I don't believe you should "force it" and go through a list of animals to find a "spirit animal".