I have a 2003 Holden Astra. I've owned the car since new when purchased from a dealer. The temp gauge is always running at a ¼, but would increase to 1/2 on a hot day or sitting in traffic on a hot day. Would cool driving on freeway. Recently the timing belt and water pump were replaced. Nothing wrong with water pump, but mechanic insisted on replacing it. Temp gauge now at 1/2 in normal operation, and increases to 3/4 when sitting in traffic. Mechanic tells me this is normal, but after my 15 years of owner operating experience, I don't think it is normal.
It’s common practice to replace the water pump at the same time the timing belt is changed because they usually need it. It doesn’t appear to be overheating, i.e. the gauge is not going off the scale, so I would just keep an eye on it and if it does show signs of overheating get it checked out.