To be fair, while the various Star Trek alien species were often assigned certain broad cultural traits, the shows took pains to show variations among each race, so they weren't all the same.
As far back as "Balance of Terror," each of the featured Romulans had very different personalities and philosophies. You had the war-weary Commander who just wanted peace and that ambitious underling who wanted battle and glory and political advancement. Not the same at all, even though they came from the same imperial culture.
Ditto for the Ferengi. Sure, the Ferengi are all about profit in general, but Quark, Rom, Nog, the Grand Nagus, etcetera all had very different priorities.
Even among the Vulcans, I think it's safe to say that Spock or T'Pol would not have done the same things Valeris did . . . .