In the Purple Rain film, this is the closing song, after the epic performance of "Purple Rain" brought the crowd to tears and assured everyone that the Kid would eventually leave that town and become the superstar he needed to be.
"Purple Rain" broke them all down. "I Would Die 4 U" builds them all back up with triumphant energy. That is how I choose to frame this song in my mind.
The futuristic pop melodies of this song, in the verse, in the chorus, are beautiful. Just so much imagination.