Hello Pete,
I went on this trip earlier this year. I must say that I was not overly impressed with what I saw of Chile. The second day tour to Valpariso is not recommended. Including terrible traffic in Santiago the whole trip took nearly 12 hours and all we saw a poet's house, an admittedly good lunch and then a quick walk through town to meet the coach and back.
The journey over the Andes to Argentina was spectacular. Highlight of Argentina was a tango show with excellent meal. Brazil was even more interesting with breath-taking views from the Christ the Redeemer statue. Hotel was particularly good (apart from the lifts) being sited right on the sea front with spectacular views along Copacabana beach.
Weather varied from very wet to very hot, but never cold, apart from when crossing the Andes.
Apart from the one reservation, a most enjoyable trip. Enjoy!