Systems and methods for performing, assessing, and adjusting neuromodulation therapy are disclosed herein. One method for assessing the likely efficacy of neuromodulation therapy includes positioning a neuromodulation catheter at a target site within a renal blood vessel of a human patient and obtaining a measurement related to a diameter of the renal blood vessel via the neuromodulation catheter. The method can further include determining a diameter of the renal blood vessel at or near the target site based on the measurement. In some embodiments, (i) one or more parameters of neuromodulation energy to be delivered to the renal blood vessel can be adjusted based on the determined diameter and/or (ii) the neuromodulation catheter may be repositioned within the renal blood vessel.