An LP only contains amplitude information. The other two elements of music--pitch and tempo--are supplied by applying the correct speed to the spinning of the record. The more consistent and accurate the speed, the more faithful the musical retrieval. By all accounts I've read or heard, the Rega external power supply improves the speed accuracy and consistency significantly. This improves the music retrieval in ways that an upgraded cartridge and phono preamp cannot. One could even argue that a negative side effect of upgrading the cart or phono stage first is that they would make any speed control issues more obvious.
