Retired in 2014

Hi, my wife and I are first time cruiser and we are interested in the 18 day Panama & Scenic South America Expedition Cruise, from Fort Lauderdale to Santiago, Chile, passing through the Panama Canal. We are looking at the two October cruises which are lightly booked so far. Has anyone been on this cruise? Is a repositioning cruise less desirable? We would appreciate any advice. Thank you.