To answer your final question first, increased access for stakeholders is a positive attribute of government because the government thus embraces and exercises democratic principles and social principles. Neither of these things are inherently good or bad, but instead require evaluation based on an individual or culture's value systems. For instance, in the United States, the populace generally believes that democracy is a good thing, so the government showing adherence to those principles is accepted by the people. On the other hand, Russia has much lower rates of popularity for democratic institutions, so the populace there may thusly be more concerned with alternate issues. Rhetorically speaking, these principles in the United States appeal to ethos and pathos (ethos: is it moral? pathos: how does it make me feel?). Social principles are a bit more nebulous because there seems to be less room for subjectivity. For instance, comparing systems of governmental succession leaves plenty of room for argument; comparing systems of punishing crimes that include extreme corporal punishment leaves less room for argument based on principles of universal human rights. Nevertheless, allowing stakeholders to access their government does at least two things on the social side: (1) it provides more "skin in the game," so stakeholders feel personally responsible for the status and upkeep of their communities, and (2) populations that lose a sense of connectedness to their government and communities are historically more prone to revolutions (consider the exaggerated income inequality of Tsarist Russia or pre-Revolutionary France).
Now, to turn to your first question, separation of powers and checks and balances provide multiple access points for stakeholders by providing more government positions and allowing them to oversee one another. An easy illustration is to consider a monarchy versus a democratic republic such as the United States. In a monarchy, a single ruler can exercise all three of the main powers of government (executive, legislative, and judicial). They can declare a law and immediately try and convict a citizen of that law and mete out judicial punishment up to and including execution. Many monarchies today are prevented from such actions by a constitution, making them constitutional monarchies. The system in the U.S., however, divides these roles into three distinct branches (separation of powers), each of which has a specified manner of overseeing the other two (checks and balances). Some of these checks and balances require special positions to fulfill them, again providing increased access for some citizen to become involved in the process (e.g. a special investigator). While not all of these principles have been followed in recent years, this is the system the Founding Fathers conceived to protect their fledgling government from tearing itself apart through factionalism, corruption, and inner strife.