Is there a point where further dilution of ethanol is not exothermic?
Mixing ethanol and water is exothermic all over the range at about room temperature. Data are available, e.g., here excess enthalpy ethanol-water

However, at relatively high temperature and at least around azeotropic composition,  the mixing should become endothermic otherwise the ethanol-water azeotrope should boil at higher temperature instead of having Bp of 78.1 °C.