Honours is better than Masters for Commerce/Arts disciplines because it's harder to get in and you won't be 'overqualified' for entry-level jobs that you could be with a Master's degree. Also, usually in a Masters you'll learn the same content as a Bachelor's degree (with the exception of maybe Macquarie's 'Master of Applied Finance' which is very strong I've heard but you need work experience before doing it), while in Honours you'll learn an extension of the content you're already doing.
Finance Honours is a good idea if (a) you need an extra year to boost your employability, (b) you want to go into research (but really who would want to research in finance, it's so narrow), (c) There are some jobs that require either Economics or Finance Honours (but Eco honours would be stronger) or (d) you want to go into a job that requires high academic excellence (e.g. Consulting).
Economics Honours is generally more highly regarded than Finance Honours, but they will send different signals to employers. If you want to go into IB and you need an extra year to take another shot at internships, you'd probably want to choose Finance Honours. One option could be to do joint Honours in Economics and Finance (know someone doing this).
