"I DO have this strange habit of layering things."  - I get you girl! I do exactly the same thing.

i'll use cream blush and top it off with powder blush.

I'll use colored eyeliner in pencil and then add a thin line in liquid black! all on the same line in the same eye.  I think it is pure genius :D... lol

Besides I too keep stuff way past the expiry date. I throw it away only when it seems to spoil.