Using a secondary anti-Strep-HRP will enhance the signal as chemoluminiscent techniques are more sensitive than signal produced by deposition of pigment by AP.

Check the manufacturer specification sheet for the secondary antibody as it will state the recommended dilution of the ab.

I agree with Xi Jiang: The use of chemiluminescent detection methods or detection methods that are based on fluorescence (based on streptavidin conjugates with fluorescent dyes) will have much lower detection limits compared to the chromogenic substrate you suggest.

Thanks for the insights J. Stolz and Xi Jiang