NOT AT ALL.
But... SYMPATHIZE. Be the character and live the character in your mind. You're right, if you do not do it well or convincingly, you can come off as a huge phoney, wannabe or (fill in your favorite derogatory name here). If you feel less than confident about something, research it, ask questions of the genuine article if you have to, and be honest about your intentions and concerns just like you are in this question. You may easily offend somebody with the mere implication you are conducting anthropological research into the natural habitat of the lower classes but that is the risk you have to take. However, if you really want, you can find people that will consider it interesting and entertaining to advise you. I for one have anecdotal experience in both the middle and lower ends of class structures and I am not offended by this question. (I also allow email contact through Y/A and if you asked me interview question for research, I would answer your questions and consider the exercise interesting and entertianing.)
Furthermore, it didn't work out too bad for Dickens, did it?
EDIT ADD: (After reading other responses) Yes, be careful with phonetic writing. (In fact I might have entirely misinterpreted your question altogether as a context of attitude and perspective, as opposed to speech.) My personal experience: I write characters that speak in cliche Russian sounding accents (all vowels long, rolled 'r', all consonents hard, etc.). I dabbled early on with phonetic spelling and ultimately hated it then settled on making the protagonist simply comment on the accent through narrative and let the audience decide whether or not they want to go through the effort of enforcing it. However, I swap the conventional English orders of subject and predicate, verb and noun (the way Russo / Slav types do when learning English, and accept that as the best I can do. With minor characters that speak no more than a dozen lines, I will occasionally apply phonetics ranging from excessive for extraordinarily provincial colloquial speech to strategically deployed single words or phrases just to suggest an accent or affectation.
(Man! Am I longwinded, sorry.)
As far as major characters that speak throughout an entire story, I personally don't like the idea of phonetics and would really limit it to the infrequent exception, supported by the occasional narrative commentary.