I think that spiral wound gaskets are overkill for the types of systems you're describing. I've always used the fibre-elastomer flat gaskets for 150# water systems like these. The cost of using spiral wound gaskets just doesn't make sense. Also, if you're in a jam, you can cut a flat gasket out of a sheet of gasket material.
For all 300#+ systems or higher temperature 150# systems, I've usually used the spiral wound gaskets.
I agree with you about people being in the habit of specifying spiral wound no matter what the application. Our company's standards specify spiral wound gaskets. I think part of the reason is it's a safe default if you have people working on a project that don't have much experience with gasket selection.