We present a phenomenological framework in which quantum vacuum fluctuations are governed by local matter density, producing observable consequences across three physical regimes: cosmological expansion, galactic dynamics, and solar coronal heating. The central ansatz posits that the effective virtual particle recombination rate is exponentially suppressed by local baryonic matter density. This suppression operates through gravitational and electromagnetic channels, resolving the energy-scale conflict between cosmological and stellar applications. In cosmic voids, unimpeded vacuum fluctuations drive accelerated expansion via a dynamical effective cosmological constant, consistent with DESI 2024 results and the Running Vacuum Model of Moreno-Pulido and Solà Peracaula, which provides the QFT-in-curved-spacetime foundation for geometry-dependent vacuum energy. In galactic halos, density gradients source a Gross-Pitaevskii scalar field with ultralight quanta mass in the range 10^-22 to 10^-20 eV/c^2, situating the model within the fuzzy dark matter parameter space. In the low-density solar corona, magnetic energy converts continuously to plasma heat at a volumetric rate consistent with observed temperatures. This prediction produces a density-switch signature — heating anti-correlating with local density independently of field topology — distinguishable from the nanoflare model and testable with existing Parker Solar Probe and Solar Orbiter data. The framework is phenomenological; the suppression ansatz is motivated rather than derived from first principles. Directions for a QFT derivation within the RVM framework, CMB compatibility testing via axionCAMB, SPARC rotation curve fitting, and a specific Parker Solar Probe analysis protocol are outlined as priority future work.