vAsanA-s can be bad as well as good. On the spiritual path (including the advaita path) we strive to eliminate bad vAsanA-s and cultivate good vAsanA-s.
In the bhagavad gItA, shrI Krishna teaches three principle yoga-s. These are karma, bhakti and j~nAna. In simple terms, the first is the obligation of everyone - even those who, as a matter of speaking, are not on the spiritual path. It is necessary for all to strive to do good action.
bhakti and j~nAna, on the other hand, are means for realization of the Atma. In this respect, we can say that bhakti is essential, since it is the way of loving God, and that j~nAna is sublime, since it is the way of knowing God.
For the adhikArin, the means of devotion and knowledge are of paramount importance. By helping us to realize Atma-brahman, these means provide the greatest foundation for the cultivation of good vAsanA-s.