I am wondering whether should I take the bus direct to Chengdu or stay one night at Songpan on my return from Huanglong or Jiuzhaigou

Hi, Munigou with very beautiful natural beauty there is worth your time and it is around 30km from Songpan town. And he town itself has pround culture and was an important military town in ancient China. You can go there to experience and feel the life of ancient Chinese people as well as the ancient City Wall. If you are not interested in neither I mentioned, you can take a direct bus back to Chengdu then.