For year 11 at least, I don't think it's necessary. Personally, the Pearson Dixon/O'Mahony textbook gave me all the info and skills I needed, along with a bit of reading the news and Plain English Economics (I think someone posts a copy of that each time a new one comes out) to supplement it. You might need to take time out of class to review the content and understand it more solidly. Additionally, there's the Riley textbook which you could use for extension, but it goes a bit beyond the syllabus. I should also mention that you might need to learn some basic content first before the news and Plain English is very meaningful.
If you're worried about handling exams, the Dixon workbook is decent for some exam-style questions. If you don't have time to do all the questions, I found that simply reading them and formulating a response in your head can be sufficient. In terms of essays, you can try asking your teacher to give you some practice questions and feedback on your essays.
If you're thinking of getting tutoring, you'd probably be better off spending that time and money on a different subject. Obviously I haven't done year 12 though, so I don't know about that. So far, though, it's about sustained effort.
