Is there a way of selecting all faces that have an angle between X and Y degrees in relation to a plane?
select >> similar >> normal ( options in tool shelf )
Thanks for answering, but I knew of that and it doesn’t really do the trick. It just selects some of the faces of similar inclination and direction. I am trying to select every face that has an angle between 30 and 90 degrees in relation to the X-Y plane, no matter the direction (or rotation?). I’m not sure how to explain it better in Blender terms, sorry. 
I don’t think Blender has a selection tool that does that right now. The best bet is to find a face that best represents the midpoint of what you’re looking for and use ‘select similar’.
Well, I ended up creating a reference sphere with as many faces as I could and L-selected faces around the diameter that seemed to have the inclination I was looking for and then selected similar for the rest of the object. It selected about 75% percent of the faces I needed, so I guess it’s one way of doing it… In any case it saved a lot of manual work.