I wouldn't call it unpolished at all. I would characterise PKD's prose as workmanlike. It's very effective, just not what anyone would ever call lyrical or stylish. Stephen King once described his own writing as "the literary equivalent of a Big Mac and fries", and there's some of that in PKD, at least on the surface level.
I do think PKD improved as a writer in the 1970s, once he kicked his drug habit and slowed down his hyperactive output; from this era, Flow My Tears the Policeman Said, A Scanner Darkly, and the VALIS trilogy all has some beautiful writing and show Dick as a deeper and more mature writer.
As for the rest of the sci-fi genre, there's a lot of talent among his contemporaries. I would especially suggest:
* John Crowley. Widely recognized as actual an Author of real Literature, though only his earliest works could be called science fiction. Start with The Deep and Engine Summer.
* Harlan Ellison. Some of his stories ("I Have No Mouth and I Must Scream", "Jeffty Is Five", etc.) are simply masterfully written.
* Samuel Delaney. He's an acquired taste and certainly gets a bit self-indulgent, but novels like Babel 17 are often beautifully written.
* Ursula LeGuin, e.g. The Left Hand of Darkness.
* Gene Wolfe. Increasingly also recognized as a genius, I also particularly like his short stories. Start with The Fifth Head of Cerberus; graduate with the monumental The Book of the New Sun, which has no equal in or out of the genre.
* J. G. Ballard. A consummate stylist, he eventually drifted away from SF, but his earlic works are fantastic. My favourite is The Crystal World, as well as his numerious short stories, including one of my favourite stories ever [1]).
Of later writers, William Gibson, China Mieville and Iain M. Banks come to mind.
[1] "Report on an Unidentified Space Station": http://geosci.uchicago.edu/~kite/doc/roauss.htm