The experience and consolidated knowledge of a warrior who had become immortal were much more useful in a short period of time than the legacy of the Star Emperor had been to Mo Wen.
The legacy of the Star Emperor and the legacy of Ji Wuya were both of very high levels. However, Mo Wen's current realm was too low, and they were too far-fetched for him and so were of minimal help.
Even though Xiang Buwei's memories were different, he was a warrior who had become an immortal in the Primordial Soul Realm. He had just gone over the threshold of the rite of passage martial arts. To Mo Wen, Xiang Buwei's martial arts experience was much easier to understand and accept.