I agree with John, if the cracks keep coming back then you need to have them looked at. I have winessed these cieling come down on more than one occasion and they make a real mess of things, A replacement cieling can be formed by 'over sheeting' with plasterboard quite cheeply, and if you want a texture coating, you needn't go to the expence of having the cieling replastered as plasterboard has 2 faces one for plastering (the dark side) the other for decorating and texture coating. Your fire resistance between floors will also be improved slightly because of the extra layer.