That's a lot to pack in to a year. We did pretty much that trip in two years!!
(Mind, we worked for 9 months in Oz)
First off, if you're backpacking I would forget about round-the-world tickets. I know so many people who bought them and then let them elapse because they wanted to spend longer away.
Thrifty is about right for SE Asia - we probably budgeted a little more, but you do spend more if you try to cram in additional travel or extra excursions.
Australia/NZ - NZ is far cheaper than Oz for general costs but you spend (or can spend) a fortune on sky-dives, etc (and the videos/t-shirts/etc.). I can't remember off the top of my head, but you'd be better off getting up-to-date prices anyhow. I think for Australia we had about $50-60/day (camping in campervan) with extra set aside for activities.
S Ameria varies widely from country to country, bolivia being one of the cheapest and argentina one of the more expensive. Again, I'd do individual checks to be sure. Also note that distances are VAST in S America (more than you'd think) and that you should budget for additional costs like flights and top class coaches (trust me, there will be times when you will appreciate these!), especially in Argentina.
For prices, etc. there's a really good website at
http://thorntree.lonelyplanet.com People on there will be able to help with budgets for individual countries.
If you need more info, PM me.