The work presents a joint design framework that combines an energy-efficient MIMO receiver architecture with an optimized power allocation strategy for spatial NOMA in miniature UAV-assisted IoT networks. Specifically, we design a low-power receiver using spatial modulation and intelligent transmit antenna selection to minimize energy usage. Simultaneously, a dynamic power allocation scheme is developed to ensure fairness by allowing all users to act as active data users in different time slots. The air-to-ground channel is modeled by considering UAV altitude, mobility, and probabilistic line-of-sight characteristics. Simulation results demonstrate that at a UAV altitude of 50 meters, the proposed method achieves a peak energy efficiency of approximately 7.8 bits/Joule, compared to 6.0 bits/Joule for traditional NOMA schemes. The system also maintains a target user data rate of 2 bits/s/Hz and performs optimally at a transmit power of 20 dBm and UAV velocity of 5 m/s. These results highlight the effectiveness of jointly optimizing receiver design, power control, and UAV parameters to achieve sustainable and high-performance communication in future 6G-enabled IoT networks.