You seem to still have a great grasp of the basics greenbelt
If you Settle a city on the resource you do indeed lose the additional benefits of building A Mine, Pasture, Farm, Plantation or Hunting Camp etc. on top of the resource.
Settling on certain resources can still give you some resource bonus typically settling metals on plains hills although there are others (there is an excellent guide with pictures in the guides section.
But as in most things in Civ it is a choice between one thing and another.
The benefits of settling your city on the resource are
- Automatically hooking up the resource you have the technology to use (so if you have Animal husbandry and settle a Horses you can immediately build Chariots and cavalry units at your new city{and any city connected to it})
- Saves the worker turns to build a worker at (or move a worker to) the new city and the worker turns to build the improvement.
- Your resource can't be plundered by units or sabotaged by a spy (a lot of people Settle on an Oil or uranium Resource to protect their power supply)
- It may let you position your city so its BigFatCross includes more/other resources or better land eg. more grasslands or less mountains.
- Denial of a strategic resource to rival civilizations
- The various benefits of having the resource earlier, immediate diplomatic trading of the resource, health\Happiness bonuses to city\empire. It is usualy more advantageous to have anything earlier in a typical civ game.
You don't say what version of Civ you are playing I am using vanilla so all the above applies.
If you are playing Beyond The Sword expansion Forts have been upgraded considerably giving you a third option. In the posts above they demonstrate one of the new uses of them and allude to another which I will expand upon
A fort acts as the appropriate improvement without giving the hammer or food bonuses.
So if you build a fort on
Bananas and have Calendar technology it counts as a Plantation as soon as you connect it with roads or a river (coast line with Sailing, off shore island/continent with Astronomy)
You can build a fort anywhere in your cultural borders.
If the fort ends up within your city's BFC you can order your workers to build a plantation over the fort so the bananas are available as soon as the fort is built and nicely protected from your foes then once the area becomes more peacefull you build the plantation and get the additional +2 food while maintaining a constant supply of bananas