Passive sensing exploiting Wi-Fi as an illuminator of opportunity has attracted considerable interest for the ubiquitous presence of Wi-Fi systems in many environments, and the relative low cost & complexity of related passive solutions. In this paper, we consider a reference-free, amplitude-based sensing strategy exploiting Wi-Fi signals of opportunity and we investigate the potential advantage conveyed by the use of polarimetric diversity on receive. Specifically, we exploit the data collected by a dual-pol receiver to experimentally demonstrate that the joint availability of the signals collected by differently polarized antennas (H and V) could remarkably enhance the detection performance of the resulting Wi-Fi sensor, even if based on such a simple and cost-effective reference-free sensing approach. Moreover, we analyze the characteristics of the target signatures extracted by the considered amplitude-based approach for either single and dual-pol receivers, in order to investigate their suitability for detecting and recognizing different human movements, in view of future applications for automatic classification.