They got the styling right, especially on the second generation version. The non-functioning rear side glass in “flying buttress” panels was a clever touch. The Fiero name and concept seems ripe for a modern reboot done right with proper engineering. The only catch might be overlap with the now-mid engined Corvette.
I think that's what ultimately did in Fiero (and by extension Trans Am, and Pontiac). GM didn't want any legitimate rivals to the 'Vette then, which is why I suspect any Fiero reboot would never come from GM now.
The timing of the Fiero may have been just a few years early, but look at all the 2-seaters that came into play around the time Fiero was cancelled - Miata, MR2, Del Sol, etc.
I think, had the GM suits let Fiero become what its designers wanted it to be, it would have been very succesful, but no doubt, would have cut into Corvette sales.