Yes, I tested them all, and they all did nothing in different ways. For example:
- in Taito Cup Finals, pressing Start on the Special Menu turns credits into powerup points whether Buy In is set to On or Off (and your points are labelled Buy-In onscreen, which suggests it's supposed to be related to that).
- in Hat Trick Hero '93, however (which is a variant of the same game), pressing Start DOESN'T turn credits into points, whether Buy In is on or off.