What is the difference between a Mufthi and a Moulavi? Is the difference measured in a spiritual or academic sense?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

If by 'Moulavi' you mean a preacher or a caller to Islam, then there is a difference (from an Islamic view point) between a Mufti and a preacher.

A preacher is required to convey [to people] the knowledge which he knows even if it is only one verse from the Quran or a single Hadeeth. The Prophet said: “Convey on my behalf even if it is only one verse (from the Quran).” [Al-Bukhari] 

As regards the Mufti, there are some conditions and requirements which should be met in order for one to be eligible to issue a Fatwa and become a Mufti. These requirements were mentioned by the scholars ; in this regard please refer to Fatwa 89691.

Therefore, it becomes clear that the difference is based on rules from the Islamic legislation.  

Allaah Knows best.