If you don't understand why cons is important, and the appropriate places to use it, then you really don't understand Lisp.
Lisp-the-mathematical-model, perhaps, but not Lisp-the-programming-language.
Conses are definitely a fundamental idea, and they're obviously how source code is written, and it's nice that they're around — but honestly for real work it's unlikely that most data will live in cons structures (unless of course the higher-level data structures actually are built from conses, which of course they could be).
I was going to suggest watching the video presentation "The Swine Before Perl", by Shriram Krishnamurthi, but alas I can't find a link to the video (which is sad, because it is a very entertaining and informative video). The slides are here: ( http://ll1.ai.mit.edu/shriram-talk.pdf ), but without the talk they may do you no good.
Hopefully someone will see this and add a link to the video ( it should be made available again, even after all of this time, it is still great -- I believe I saw it as recently as 2 years ago).