Universities will give +2 science for leaving them unimproved. Each citizen gives +1, so in a city with a Library and University, each citizen is producing 2 science ((1 + 0.5) * 1.33). Public Schools will benefit the citizen but not the jungle tile, and you can't put a trading post on bananas.
The plantation will add +1 food to the tile, so if that extra food will let you get another citizen and you have the happiness you break even on science. The citizen itself can work a tile or be a specialist, of course.
So, yes, the extra growth can be worth it given:
* You have the happiness
* You have the worker turns
* There aren't enough good tiles without improving the bananas
* The additional +1 food will result in an additional citizen