I agree, this isn't likely going to be a huge gain. I certainly don't recommend it as anywhere near a first mod. This is planned for a fairly modified car. I wouldn't even consider it unless you at least have an alternator delete done already. Also, its an idea that I hadn't heard of talked about here. Instead of spending a few hundred dollars on a pump, this costs under $100 with new parts, and can be salvaged for much less.
Its not just about the efficiency gain either. There are other benefits like having heat when the engine isn't running and being able to cycle the pump when the block heater is plugged in. It will pair well with my idea of
using engine coolant to speed up transmission warm up times, especially with my short commute. It'll also free up a bit of horsepower at higher rpms which never hurts. So, it pays real well with other mods. If you don't have any of those other mods, it probably won't help as much.