Well, political philosophy is by itself a very fascinating (and often overlooked) subject. That said, it's not very likely to see it applied to the practical levels when a certain country's politics are based on personality or saying what the people wants to hear. I'm currently reading "Fear and Loathing on the Campaign Trail 72", and I think that serves as a practical example of this. I know quoting Hunter Thompson is strange (and perhaps I should be using actual philosophers), but here you have Muskie, Humphrey and Nixon characterized as people who make up their own convenient truth to be elected, and the people proceed to choose which "truth" they like the best, while McGovern (supposedly) is the only one who says things that are close to the so called objectivity (therefore the only "honest"), and thus the one people avoid.
Now, going to the specific points you mentioned, I found the modern view you mentioned interesting in the way that it persists on creating good and bad. I accept having a degree of "objectivity" (that is, the so called common sense) on ordinarily life in order to make things simpler, but it's impossible to separate objective good/bad from subjective points of view. Here's a flawed example: If idea A is good and I believe on that idea, then that automatically makes me good. It's a argumentative fallacy, but it's bound to happen. That leaves us with the "material" role, which has a potential to reach objectivity. But once you combine both roles, you are left with some tough choices: Should we accept all material evidence as objective, and discuss only how to interpret it? Should we take everything as subjective and therefore disregard reason? Or perhaps accept objective evidence and a determined set of beliefs as the correct answer?
I agree with you, politicians represent interests, and the way we have of holding them accountable is very flawed and (ironically), subjective. That's why Ronald Reagan goes free after Iran-Contras and Watergate destroys Nixon. It wasn't the truth that destroyed them, it was the subjective truth/narrative that won the battle of perceptions. Some people can do this and be branded as bad, others can do the same and be good.
That is my basic problem with political morality, the fact that the absolute objective truth is an utopia. We are left with a very uncomfortable decision (which most people ignore and cynical people - like me - struggle to comprehend) between having determined sets of beliefs for determined situations, a set of beliefs that encompassed everything, thus simplifying political issues to make it a discussion of details instead of ideas, or trying to handle the variety of ideas in order to come up with something somewhat democratic, but unrealistic and chaotic.