  This paper provides sufficient density conditions for the existence of smooth
vectors generating a frame or Riesz sequence in the lattice orbit of a
square-integrable projective representation of a nilpotent Lie group. The
conditions involve the product of lattice co-volume and formal dimension, and
complement Balian-Low type theorems for the non-existence of smooth frames and
Riesz sequences at the critical density. The proof hinges on a connection
between smooth lattice orbits and generators for an explicitly constructed
finitely generated Hilbert $C^*$-module. An important ingredient in the
approach is that twisted group $C^*$-algebras associated to finitely generated
nilpotent groups have finite decomposition rank, hence finite nuclear
dimension, which allows us to deduce that any matrix algebra over such a simple
$C^*$-algebra has strict comparison of projections.
