<p>In the context of new power system construction, effectively mitigating and compensating for power fluctuations in distributed energy units—while overcoming market access barriers that hinder the participation of small-capacity distributed units in electricity spot markets—holds significant research value. To address the limitations of existing studies, which often focus on single-timescale optimization or fixed penalty coefficients, this study proposes an optimized operational strategy for energy storage aggregators targeting small-capacity distributed energy units in electricity spot markets. Specifically: (1) a multi-level day-ahead and intraday trading framework based on contractual cooperation is constructed, integrating coordinated mechanisms for both revenue allocation and power distribution. (2) An innovative willingness-to-trade mechanism for energy storage aggregators is developed, leveraging electricity price forecasting curves and real-time pricing trends to determine a fuzzy feasible domain for actual power output through weighted calculations. (3) A bidirectional segmented penalty mechanism is introduced, defining penalized baseline outputs and penalty criteria. Aiming to maximize aggregator profits while ensuring operational safety constraints, including unit stability, independence of energy storage systems, and compliance with grid parameters. The proposed strategy utilizes an improved fruit fly optimization algorithm to determine the optimal power output within the fuzzy feasible domain. Simulation results demonstrate the effectiveness of the strategy in enhancing aggregator profitability by about 11.7% and improving the quality of grid-connected power by about 5%. This provides both a novel coordination framework for multi-timescale market participation by small-capacity distributed units and an innovative pathway for advancing the energy transition and optimizing grid integration quality.</p>