If you have completely explored your world when 1.8.2 and 1.2.3 come out, then yes, you will need a whole new world.
If you haven't explored your world when 1.8.2 or 1.2.3 comes out, you will be bale to find the new terrain features in the unexplored areas. It's just like how clay spawned into peoples worlds after the bug fix patch.
Only if you want new biomes/ bigger world/ end portal/ etc.
You will still have endermen/ ocelots/ etc. in your world.
If you have completely explored your world when 1.8.2 and 1.2.3 come out, then yes, you will need a whole new world.
If you haven't explored your world when 1.8.2 or 1.2.3 comes out, you will be bale to find the new terrain features in the unexplored areas. It's just like how clay spawned into peoples worlds after the bug fix patch.