Group-VB transition metals exhibit unusual high-pressure electronic and structural responses associated with partially occupied d states. In vanadium, pressure-induced softening of the shear elastic constant C44 accompanies a BCC–Rh structural transformation, but the relationship among electronic evolution, elastic softening, and phase stability remains unresolved. In this work, using first-principles calculations, we construct pressure–composition phase diagrams and C44 maps for V–X alloys (X = Ti, Zr, Cr, and Mo) over 0–15 at.% alloying and 0–300 GPa. We find that the alloy-dependent evolution of C44 broadly tracks the BCC–Rh phase stability boundaries, while the detailed characteristic pressures are not identical. By analyzing the Band-6 Fermi-surface nesting evolution, nesting vector qn, and near-EF band shifts, we demonstrate that dilute alloying systematically tunes the nesting-related electronic topological transition (ETT). Specifically, alloying with Zr provides the strongest delay of the Band-6 ETT, C44 recovery, and Rh-to-BCC reentrance, whereas Mo demonstrates partial decoupling between the Band-6 ETT and phase stabilization. These results establish neighboring-transition-metal alloying as a route to tune near-EF d-derived electronic structures and clarify the distinct but correlated roles of electronic topology, elastic response, and thermodynamic phase stability in compressed V-based alloys.