Hmm.
In my personal opinion, reading for pleasure is not going to really "help" you as much in terms of marks as study guides would. Reading David Eddings is NOT going to spoon-feed you the Jacobean Tragedy elements found within Hamlet, and by the same token, reading Harry Potter isn't going to help you understand prose fiction either.
But - I am a profilic bookworm. Even through the HSC, I didn't really stop. In blunt terms, the best thing it did was make me read my prescribed texts, many of which I found dull - but since I love to read, it kept me going.
When you read a large number and variety of books I think you tend to "notice" things a lot better - such as a particular tone the author is establishing, or little things that aren't normally there/are there that aren't normally there etc etc. The ability to analyse a text without the use of study guides, for example, is one of the things that can develop with wider reading.
Silvermoon stated most of the benefits of wider reading - such as improved vocabulary and a greater understanding.
I think with the Advanced English course, you can get a Band 6 with the help of study guides and many critiqued practice essays (or at least, I did), but to get a really good mark (particularly for EE1 and EE2 people), then I think you really do have to do some reading to gain a better understanding of literature and how it is used... you can "know" it thanks to study guides, but you won't really understand it until you're able to apply what you know to things you read for pleasure
![Stick Out Tongue :p :p](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)