As-salamu 'alaykum Shaykh Gibril Haddad (hafidhahullah) has made a good takhrij of these hadith, you can easily find his article on livingislam I think. By the way, if you look in fiqh manuals like Nur al-Idah, where Imam Shurunbalali has mentioned them in the chapter of Hajj, they are used as evidences for visiting al-Madina al-Munawwara. This clearly shows that they have relied upon by our 'ulama for centuries... Allah Hafiz
in their individuality no, (if i'm not mistaken) some ahadith, in virtues of visiting RasoolAllah ŞallAllāhu álayhi wa aalihi wa sallam are hasan, and some dha'if, but collectively, they reach the status of 'hasan, and aimah arbaá (the four imams) have acted upon them, so the acceptance of aimah-e-deen has also elevated their rank of authenticity and rigour. 'Hazrat Sayyed 'Alawi Maliki alaihi rahma wa ridhwan discusses it in deail in his master piece 'shifa ul-fuwad bi ziarati khair al-íbaad. urdu translation Dar-e-Rasool Ki Hazr by Mufti Muhammad Khan Qadri.
are these hadith sahih? whoever visits me, my intercession is wajib for him whoever does hajj and does not visit me he has transgressed against me