I am also trying to install Visualizer into Sketch Up Pro 2016, I have been using it in the past for Sketch Up Make 2015. I've tried following the instructions above but my results are slightly different.
Firstly, when I go "Finder", then "Applications", My Imagination Visualizer app sits on its own within the applications folder, it's not within my Sketch Up 2015 folder. I've tried copying just the Visualizer app but it doesn't register when I open SU 2016.
In "Preferences" within Sketch Up 2016, I've tried "install extension" and it maps me to my apps folder, but I'm not able to select Imagination Visualizer as it's greyed out. Also within this Preferences box, Visualizer is not listed in the list for me to tick.
Worth noting that I'm on a Mac and I a currently using a free trial of Sketch Up Pro 2016.
Can someone please advise?