There's been a lot of good suggestions already, so I'll just discuss my personal thoughts.
I've done a lot of travel in the last couple of years. Nearly all of this has been with a 30D. Everyone above is right. A 5Dii is "better" than a 450D. But I look back at my photos from a crop camera and I don't feel any regrets. I love the ways my photos have turned out. If you look in magazines and on the net, some excellent photos are taken with a 450D. The only reason I'd consider changing is if you are doing a lot of low light photography as the 5Dii has a clear advantage. The other significant advantage of a full frame camera - shallower depth of field - is less relevant for travel photos. Usually, you don't want to blur the background totally. Instead, you'll want to leave a hint that you are somewhere exotic. Crop cameras can actually do this better, as you can use a wide aperture and still have more of the background in focus. I'd only consider changing cameras if your finances are in top shape. If you're concerned about having enough spending money, save it so that you can have more fun.
South America and Central America scream wildlife photos to me. Are you sure a 7D with a 1.6 crop factor and great autofocus isn't a better option? The 7D also has more weather sealing, which might be useful if caught out in a storm.
Until recently, my usual travel kit was a 30D, 10-22, 50, 70-200 f/4 IS, plus batteries, charger, filters, flashes, memory cards, tripod, laptop, small external HDD. I'd be prepared for nearly everything except serious wildlife photography. But after the second or third day, I'd generally have the same thought - "NEXT TIME I WON"T PACK SO MUCH!!" (Although I still haven't learnt...). It seems that you’re planning on taking more than I would, so I'll just mention two problems. First the weight. You've travelled to South America before and must know about the 35 degree heat and 100% humidity. Are you sure you want to carry another 5 - 8kg of camera and computer gear?
The second problem is the stress of taking it all. You can't take it everywhere with you all the time. There will be occasions when you will want to go to dinner, nightclubs, or a carefree walk around town. That often means leaving your camera gear and laptop in your hotel room. You'd be very unlucky to have problems, but if you're like most people, you'll worry a lot about it and it will spoil the trip a bit. A lot of people end up with a small day pack that they take everywhere. But that idea gets very tired very quickly. My solution is to store expensive gear amongst my dirty socks and laundry. Or to stash it on top of a cabinet or under a drawer. No thief would ever think of looking there....
Also, get more opinions about taking a tripod. The times I use mine, it’s invaluable. They're really useful for taking self-portraits in remote locations when you’re on your own and photos at night. But they are heavy and take up a lot of room. With a bit of ingenuity, you can often find another way to brace your camera.
Therefore, my “Do what I say, not what I do” advice would be to take less stuff and reconsider any expensive new purchases.
Also, you haven’t mentioned if you’re male or female and if you have a wife or a girlfriend. If you don’t have one, I’d ditch the new lens and get a wife or girlfriend as an accessory. They can be really handy as they almost always carry handbags. Each morning can start off with the same conversation. “Honey, do you mind if I put the 70-200 in your handbag”. This also allows you to double your carry-on luggage allowance. If you're a girl, just find a boyfriend that's chivalrous enough to carry your camera bag everywhere for you. (If you don't have a boyfriend or girlfriend to take with you, make it your first priority to find one upon landing and they can also act as a a tour guide and interpreter.)
Even better, get a baby. Strollers are really useful for transporting equipment around town. Plus they will also increase your carry-on allowance. Even better, with the exception of some minor fees, they generally fly for free. I can't think of any downsides to taking a baby on a six month backpacking trip through South America.