It depends on a lot of things really
How old are you? do u crave speed? What would you like to do to it? Can you afford to spend money on something that does not pay you back with money, just smiles
In my opinion i would say,if you like your corsa and would like to keep it then swap the engine for a calibra lump and really smarten it up inside and out.
If not then swap the car for something bigger, faster and just better
If you just plan on "chavving" it with a set of lexus lights and 3 spokes then i would say leave it standard.
The 1.2 lump will pack up sooner or later so if you are not willing to do an engine swap then dont waste money on bodywork on a car that will die soon
My 2pence worth