hmm, now I faced the same issues as yourself tbh, I could 'cut my losses' and pay more for an alternative car, however, I'm sticking with it, and so far the last round of fixes Abarth/Fiat did, seemed to of fixed the problem.
How much warranty is left on the SS?
The end of the day, its your choice, but the car you bought from the dealers MUST be of satisfactory quality and fit for purpose, if it still have warranty left or not.
Personally, I wouldn't get the Evo, who knows, you could end up with other issues.