Imam Ali al-Hadi al-Naqi
Alī ibn Muḥammad ibn ‘Alī (Arabic: علي بن محمد بن علي; 829-868 C.E.) was the tenth of the Twelve Imams after his father Muhammad al-Jawad and before his son Hasan al-Askari. He remained in Medina teaching until the age of 30 when he was summoned to Samarra by the Abbasid caliph Al-Mutawakkil. There he was treated roughly by the caliph and his successors until, according to Shiite accounts, he was poisoned through intrigue of Al-Mu'tazz the Abbasid caliph, in 254/868, and was buried in Samarra.
It is called Ziyarat Al-Jami'ah Al-Kabeerah الزيارة الجامعة الكبيرة.
It is one of the most authentic and greatest in contents and richest in knowledge.
I am not personally aware of narrations specifically encouraging the visiting of those sites. (Someone may correct me!) However, there are ziyarat texts narrated for them.
However, there are narrations encouraging the visiting of all of the Imams, which would include them, and it is good to go and pay respects as a gesture of loyalty and to help maintain a tie with the history and people who once walked there and were laid to rest there. Some people might also want to go as a form of resistance to the oppression that Shi'a face today and to make a stand to show that we will not be afraid to go, and that is also good.
That being said, there are a lot of narrations emphasizing visiting other places, such as Mecca, Medina, Karbala, Najaf, and Mashhad, so I would personally place the emphasis on visiting those places first.