There is no clear cut answer to this and I guess lots of people won't agree with my opinion.

First of all, my impression is that the Master in Finance programs in Australia (my observation is based on UNSW and UWS - can't speak for the rest) are not really tough if you are a good student. I.e. some of the courses in the Master program do not significantly differ from the one in the Bachelor, apart from that the Master requires you to work more independently. My statement is based on some exams that I was grading for courses that were both offered in the Bachelor and the Master program. This is quite different in other countries (I am from Europe) where the Master is more challenging in general.

In contrast, you have to take PhD level courses in your Honours year. They are more demanding but also more rewarding in terms of what you can take out of them. The problem with Honours is, that while it is hard to get into in Australia - i.e. you have to be among the very top x% in your year - this is not the case in other countries. In Europe, many Bachelor programs include a thesis and automatically give you an Honours degree. The thesis is usually worth as much as two classes - while it has an equivalent workload of four classes here.

So - if your objective is to learn as much as possible and you are being offered to do Honours, then you should go for it. It is challenging and you keep the door open to enter a PhD afterwards. If you want to brush up your CV, then it is a trade off. I guess in Australia, the employers know about the value of an Honours degree but if you consider working at some other place that might be different.