Bitumen, the primary binder in asphalt concrete, lacks sufficient resistance to prolonged mechanical and environmental stress. To improve its durability, styrene-butadiene polymers are commonly used, although they are prone to oxidative degradation and phase instability. This study proposes a nanostructured approach to enhancing the stability and performance of polymer-modified bitumen (PMB) through the synergistic use of multiwalled carbon nanotubes (MWCNTs) and hydrocarbon plasticizers-specifically, selective oil refining extracts (SORE) and vacuum distillates (VD). Short-term oxidative degradation was assessed using isothermal RTFOT aging at 153, 163, and 173 °C. A classical first-order Arrhenius kinetic model was applied, with dynamic viscosity serving as a rheological proxy for SBS network integrity. Nanomodified compositions exhibited a 6-7-fold reduction in degradation rate constant (from 13.97 × 10⁻⁵ to 1.98 × 10⁻⁵ s⁻¹) and a 25-60% decrease in the preexponential factor, indicating suppressed molecular mobility and enhanced network cohesion. Performance was validated on SMA-16 specimens, showing up to 240% improvement in shear adhesion at 50 °C and 27% higher water resistance. Rutting resistance also increased, with rut depth reduced to 1.6–1.8 mm after 20,000 loading cycles. To integrate physical, mechanical, and durability characteristics, a set of Partial Quality Criteria (PQC) was developed and used to calculate a Generalized Effectiveness Coefficient (GEC), supporting multi-criteria optimization of asphalt mixtures. These findings confirm that nanostructured dispersed systems based on MWCNTs and hydrocarbon carriers not only delay oxidative degradation but also ensure multifunctional performance gains critical for high-traffic pavement applications.