  Nanoscale inhomogeneities and impurity clustering are often found to
drastically affect the magnetic and transport properties in disordered/diluted
systems, giving rise to rich and complex phenomena. However, the physics of
these systems still remains to be explored in more details as can be seen from
the scarce literature available. We present a detailed theoretical analysis of
the effects of nanoscale inhomogeneities on the spin excitation spectrum in
diluted magnetic systems. The calculations are performed on relatively large
systems (up to $N$=$66^3$). It is found that even low concentrations of
inhomogeneities have drastic effects on both the magnon density of states and
magnon excitations. These effects become even more pronounced in the case of
short ranged magnetic interactions between the impurities. In contrast to the
increase of critical temperatures $T_C$, reported in previous studies, the
spin-stiffness $D$ is systematically suppressed in the presence of nanoscale
inhomogeneities. Moreover $D$ is found to strongly depend on the
inhomogeneities' concentration, the cluster size, as well as the range of the
magnetic interactions. The findings are discussed in the prospect of potential
spintronics applications. We believe that this detailed numerical work could
initiate future experimental studies to probe this rich physics with the most
appropriate tool, Inelastic Neutron Scattering (INS).
