In the superb new Honolulu Zoo history book there is a photo from 1949 of Black-Handed Spider Monkeys in this exact same exhibit...almost unchanged from how it looks now. The wooden platform has been added since that time period but the rest of the cage is practically identical. Interestingly enough the zoo had 600,000 visitors in 1949 and these days receives 600,000 annual visitors even with the enormous population growth on the island of Oahu.
I'd like to see this part of the zoo (primates, purple on the map) get entirely renovated into something like a building with viewing windows into large netted enclosures that could also be viewed from the outside.