I think people think too hard when it comes to layering. Instead of purposely digging into sounds with the intension of layering, just find good sounds. It never fails.
In the end something's gonna be layered over the top of something(basslines commonly ride over kicks, strings often come in over melodies for choruses, rythm guits are used to spice up tracks, ect.), but "layering just for the sake of layering" is an excercise in futility. Alot of people say "layering makes sounds fuller" simply because they've yet to master chords.
I listen to music all day from the 1400s to present, every genre, I don't hear too much "purpose layering". I do hear different instruments hitting in unison, but in order to get the full effect of that, things have to solo out, fade in/out, have variations in melodies, but match up well, ect. Therefore, if it don't sound good on it's own, it won't work.
It's not just about playing 2-4 sounds in unison note for note.