Great results mate, would you mind sharing your results with us
In my opinion I would opt for the Monash Degree.
1) If I'm unsure of exactly which stream of Engineering I'd like to do, does Melbourne offer some time to make this decision or would I have to decide what my masters will be fairly quickly?
Under the Melbourne Model, each semester you will do 3 "Commerce" subjects and in-place of your breadth subject you will enrol in your "engineering subject". Obviously you will begin with your basic Maths and Physics. AS the course progresses you with have to make a decision, and begin choosing subjects from a certain field such as Electrical (Like me ^_^) They could include Electrical, electronic, communications, computer. So I'd say you have plenty of time to choose.
2) In terms of employability, I've heard that a Masters degree is almost essential should I want to work overseas, and I've also heard that Melbourne's engineering graduates are less employable than those from Monash, is there any truth to this?
Interms of woking overseas, I am sure that Monash and RMIT and probably other engineering courses should be Accredited by Engineers Australia, in turn giving then the Washington Accord Approval
http://en.wikipedia.org/wiki/Washington_AccordMelbourne however are still in the process of being accredited and could be eventually declined.
Also Australian certificates are usually very convincing and hold High Value overseas, especially in Asia and the Middle East overseas anyway. In the case of employability, Monash or RMIT or Even Swinburne graduates may have better chance of employment due to the nature of the UoM degree. Essentially its rushing through engineering in 2 quick years.
Will a degree from Melbourne open more doors for me or does it make no difference? (This is a key concern of mine, the possibility of missing opportunities)
I think that a degree will open one door, but your own hard work, ambition, perseverance will open the rest.
4) Should money factor into my decision? (As stated previously, melbourne will be a bit cheaper even with both scholarships on offer)
Assuming your an Australian local and will get a CSP, you should worry at the price at all. After you graduate and begin earning about 44,000 per year then the ATO will begin taxing you at a certain rate, which is 4% extra then your normal tax rate when earning 44,000. So essentially you should not really worry about money at all.