Good points. I would like manual mode in combination with Auto-ISO, but my stupid old cameras don't have exposure compensation in that mode which renders it useless for me ...

Well, that depends. Let's say, you've set your ISO and your shutter speed to fixed values. If the exposure indicator (or perhaps you call it exposure scale) indicates let's say an exposure of negative 2 (too dark) and you open the aperture by 2 stops so that the exposure indicater points to "zero", than the exposure can depend on the metering mode. If you use spot metering and the spot points to a dark area of your subject, let's say a black sweater, than the metering will be different from the evaluative metering which takes into account not only the black sweater but also the face and the background. If you just set ISO, shutter speed and aperture to some random values, the metering mode doesn't matter. However, depending on the lighting situation, your exposure could be way off. For example, inside a not so well lit room a combination of 1/1000 s, f11 and ISO 200 will result in a completely black photo. I hope this helps.