Nancy's mother's drinking problem holds another layer besides straightforward self-medication when you realize that alcohol actually prohibits REM sleep.
Tina mentions that nightmares sometimes foreshadow earthquakes; exactly what signifies Freddy's presence in Wes Craven's New Nightmare years later.
Nancy is rightly outraged when she realizes that her father used her as bait to draw out and arrest Rod...but it could easily be this incident that gives her the idea to pull the exact same trick on Freddy in the climax.
