I'm guessing the relevant comparisons are from cars around the time period before the Fiero was produced since the topic is the M1. The M1 had actually ceased production well before the Fiero was produced. However, I see more Lotus Esprit in the M1 than I do Fiero, and subsequently relate the Esprit more to it. Although both cars are very long if you see them. Quite some time ago I got to see an M1 in person, I remember it was quite long looking, and it's very similar to the Esprit when you see them up close.
If I could compare the bumper pad Fieros that appeared in those early ads to anything, it would probably be the FIAT X 1/9. Oddly enough, FIAT stopped factory production of the X 1/9 in 1982, before it was then picked up by Bertone to be manufactured until 1989 - a year after the Fiero ceased production. Crazy thing though is it's very hard to find a good conditioned X 1/9, while it's not overly difficult to find Fieros in good condition.
Now remember I'm considering PRE- 1984 model cars. Obviously more comparisons could be draw to cars built post-1984, like the MR2.