Mirage was lower-end but not bottom. Nomade was a step lower. Not sure about '74 but a few years later ('77) when I bought a Nomade the Mirage had 2 tone paint, better shifters (the SunTour you mentioned opposed to steel Huret) and quick release wheels. Same 1020 frameset which is hi-ten.

On a '74 model you're looking at either Swiss or French threading which makes replacement parts fun but if the bike is as clean as you say the headset and BB probably only need re-greasing, not replacing.

Motos have a deserved reputation for really nice paint & decals even on lower models so if yours is well preserved it should be a pretty bike.