My home park is the Cleveland Metroparks Zoo. Are you reading this, Dr. Kuhar?

Alterations are grouped by section...
Australian Adventure...
...Add a dual, large-tank aquarium building replacing the non-functional playground between the Tucker Court picnic pavilion and dingoes. Cut into the hill behind it if need be. One tank is a Great Barrier Reef tank, the other, a spacious shark tank.
...Take the doghouse out of the dingo exhibit; I realize it is shelter/protection, but it makes the species look less-impressive, like a domesticated dog.
Africa...
...replace the overflow parking area between the Vet Center and Big Creek and create a "Predators of the Serengeti" exhibit. Koepe-theme it (think Ft. Wayne Kids Zoo), and add Cape dogs, hyenas, bring the cheetahs down from PCA. Maybe relocate your lions there.
...I know it is sacrilege, but remove the historic Monkey Island, along with it's adjacent building and leopard enclosure. Expand the black rhino range (and our successful breeding program!). Bowtie it with another barn for white rhinos and/or couple it with an okapi enclosure.
...install an exhibit similar to the hornbill (?) aviary that the Indy Zoo has (the multi-species glass enclosure on the trail between their cheetahs and elephants) on the pathway to the African Plains exhibit. Give visitors something between exhibits. While we're at it, make the entrance to the African Plains exhibit more-prominent!
Northern Trek...
...Replace the arc of the sea/sea Lion, polar bear and grizzly pits with a new themed exhibit. Ideally, a new polar bear and seal exhibit with underwater viewing would be nice, but a new grizzly enclosure a la Columbus would be acceptable.
...I know the onagers are a critical species, but replace it or the camels with northern plains species like buffalo and pronghorn. Just seems like a better thematic fit.
...after you exit Wof Wilderness, how about a wolverine enclosure embedded into the exterior hill? (Across from the reindeer.) Again, think Columbus.
PCA...
...where do I begin? There is a dark side of me that likes PCA a little, but I know it was practically outdated when it opened. Proud of our primate collection, how about nuking it and replacing it with Cat and Primate Building 2.0. (Sorry, fish lovers.)
...that said, I would take the picnic area between the Treetops Cafe and employee/back entrance and create a new gorilla exhibit. I enjoy the moated openness of Cincy's Gorilla World and Taronga's gorilla exhibit. Couple it with a friendly indoor viewing area (a la Toledo) for Cleveland's long winters. My other thought was an indoor, moated greenhouse-style gorilla exhibit. Face it south for max sun, keep it lush and toasty twelve months a year.
Waterfowl Lake...
...replace that goofy rope playground with a carousel and toddler stream like Toledo's. Oh, wait!

But, don't wait to get that party area and restroom up there, like I saw on the extended site plan!