Let me just assure you, its really not the end of the world !

I personally know people who got atars under 30 or were happy getting 50 or 60, so you did do very well.
Repeating is a very bad idea, back when i was in VCE (last year) we discussed it in some length on these forums, you might want to search for the post.
I'll quickly summarise some points why:
1) If you're doing the same subjects over again you're likely to get very bored. If you're not, you might be really burnt out after this year.
2) You'll have to make completely new friends
3) Most of your mates will be at uni and you won't, you'll also put yourself a year out.
4) What if you don't get much higher? You've already wasted a year.
5) VCE is a really really draining experience, uni is significantly more laid back, do you really want to put yourself through that again?
I think you should go to uni.
If you choose a similar degree (eg commerce at la trobe/business at monash) they'll credit you as doing those units, so you don't have to do them again. If you're lucky once you finish your first year of commerce say at la trobe, you can transfer into 2nd year at monash, because you already covered all the first year stuff. Where as if you randomly choose something totally unrelated like..fine arts, you won't get credit for any of those subjects (except maybe as electives) so you'll have to do the first year commerce subjects.
Another option (as you have stated) is to pick up something like arts, do well in that for a year, then internal transfer to Arts/Commerce at monash.
Just make sure you actually want to do arts though, don't want to be stuck with something you don't like.
Now my little standard rant about universities - Really, most universities will teach you all the same thing. One doesn't have drastically better teaching quality than the other. It's not like the professors at UoM have some hidden knowledge that the professors at La Trobe/Rmit/Monash/Swinburne dont possess. They're all PhD's and getting a PhD isn't exactly a walk in the park, they're still some of the best of the best. So, i wouldn't worry too much where you end up, teaching quality wise anyway.