I learned to read at the age of four, and have always been a voracious reader. One of my major subjects at university was English literature, and my specialisations were epic poems and the works of Thomas Hardy. I have read most of the English-language classics. When I learned Swedish I did the same. I tried to read as much classic literature as possible.
But I also read fashion magazines, frothy romances, airport blockbusters, and the Daily Mail. What improved my Swedish more than anything was reading contemporary crime and romance novels.
Coming from a country where illiteracy is high, and working as an English teacher to non-native speakers though, I say read whatever you want. There are snobs in every area of life, and they think things can only be done one way and every other way is inferior. These snobs are missing out a lot in life.
Reading improves syntax, the use of prepositions, vocabulary and reading comprehension. So if the only thing you enjoy reading is light romance or recipe books, read away!