I just arrived in buenos aires from new york. Also on a KLR. Great trip. Well worth doing. But some things I'd do different next time.
1) I'd skip the US. Not to fond of long flat paved roads, and I'd lived there so long that didn't get a lot out of 'seeing' the place.
2) Shipping is costly and a pain at the best of times.
Next time, if I didn't already have the bike in the americas, I'd buy one there. If heading south, in Guatemala where the prices are pretty good and parts readily available. Plus you get central america plates and ergo very easy, free border crossings.
If heading north, chile sounds like a good place to get a bike, and i saw a few in lima with good price tags.
If you got your heart set on going to the us, buying a bike there has got to be considerably cheaper than what you'd pay in africa. I bought my KLR on ebay for $2100 and am very happy with it. (Though not sure it is still happy with me)
Either way. Get yourself some decent riding gear, a good stove for roadside coffee/meal stops and leave your tent at home, or get rid of it when you leave mexico.