I have heard many times from many people that politicians don't care about us. They say they only care about themselves, about getting elected, about staying in power. They channel their inner Hilary Clinton and ask "what difference does it make" when it comes to who they vote for. They figure a vote for candidate A is the same as candidate B. Each candidate says what they need to say to get elected, and then get to Washington to look out only for himself. People use this to rationalize their apathy, to explain why they sit at home instead of going out to vote on election day.
Let's assume for a moment, that "they" are right. Let's say that politicians don't care about us (call me naive, but I believe that some still do). Even under that assumption, however, I would argue that it does matter. I would argue, even if politicians are entirely motivated by self-interest, it would make more sense to vote for the conservative candidate every time.
Conservatives want to create a society that rewards success. They ensure their own political success by cultivating a successful economy. They know that if the economy is booming, people are happy. If people are happy, they stay in power. In a booming economy, it is easier for the Average Joe to succeed on the fruits of his own labor. If Joe Sixpack is doing well, chances are the Conservative, business-minded politician is doing well. So while he may not necessarily care about "us", he at least realizes that our success correlates with his success.
Liberals, on the other hand, want to ensure their success by creating an entire class of people dependent on them. In order to do this, they are willing to make decisions that are fundamentally detrimental to the country. They are willing to grant amnesty to millions of illegal aliens. They are willing to spend billions of dollars we don't have on "entitlement" spending. They are willing to pass stifling regulations on small businesses. Any rational and responsible individual in power would realize almost immediately that these actions are not good for a country. It is my belief that most of our liberal politicians today don't really agree with these policies. However, they are willing to pass this legislation because they know it will ensure their victory. It will keep them in power.
So, yes, it does matter. One group believes success brings success. The other group does all it can to suppress success to ensure their own. So even if neither group cares about us, wouldn't it be better to err on the side of caution and support the group whose success would most ensure yours?