Clones and Mothers

Is it better to keep the same mother alive for over a year or is it better to replace her with a clone of herself? Ive got a romulan mom that is a little over a year old and I think she is losing vigor. The clones I take off of it seem to grow better than the mother does. I know its not root bound or having any nute problems. Im thinking maybe its just old and tired? Also, is it true that once you get to many clone generations from the mother that the plants diminish in quality? i.e. will a clone of this mother produce equal quality cuttings as the original mother?