NH2- and Primary Alkyl Halides: Sn2 vs E2
IIRC, Sodamide is generally insoluble, except in liquid ammonia.  And why do people like to prepare amines with ammonia as a nucleophile?  The basicity complicates things, as does the fact that the primary amine initially formed will react further to give secondary and tertiary amines, even quaternary ammonium compounds.  It's not a reaction useful in preparative chemistry.

That said, the balance of nucleophilicity and basicity is also influenced by the solvent.  It's well known that KOt-Bu acts mostly as a base in THF and mostly as a nucleophile in DMSO, there's plenty of examples in the literature.  Hydrogen-bonding solvents tip the balance towards elimination.