Questions about the plot...

I think they were just nightmares forshadowing the bad things to come in his life - maybe not directly, but just an indication that things were going to get very bad for him. (Plus, Robert Rodriguez filmed them as a cushion in case the final cut of the movie wasn't long enough - he would just insert longer dream sequences to extend the running time. Turns out he didn't really need to, though.)

-Ry

In the book, Rodriguez said he shot the dream sequences because the movie was really short. the inspiration for one of the sequences was the really cool fake head he had.

One of the themes of the movie was the fact that he all he ever wanted to do was be a Mariachi, but he's been forced by circumstances to become this killer despite his essentially gentle nature. The dream sequences sort of reinforce that inner conflict in a way the rest of the movie doesn't really touch (except maybe the scene after he kills a man for the first time). Granted, character development isn't really a huge part of this film, but one of the underlaying themes is undoubtedly one of lost innocence.

Well in my opinion those dream sequences are referring to intuition as opposing to the 'technology age' that El Mariachi condemns.. Just as the guy that represents a whole 'mariachi band' looks pretty silly, hilarious..

Yeah the jail was a somewhat base. Did you notice that they just walked out of their cells taking off an already opened padlock.