I periodically hear the argument that the two major political parties are the same and it doesn't matter which one of them wins. That argument has been around a while, back in 1968, George Wallace said there wasn't a dime's worth of difference between the major parties.
Today, the Supreme Court handed down two major decisions, both on 5-4 votes. In one of them, they held that closely-held corporations with a religious objection to contraception can't be forced to purchase health insurance for their implies that includes contraception. In another, they held that quasi-public employees can't be forced to join a union. In both cases, the 5-4 split had all the Republicans on one side and all the Democrats on the other.
Without getting into the merits of either decision (neither of which I've finished reading yet), let me just say that if the two seats now held by Roberts and Alito (both George W. Bush appointees) had instead been filled by John Kerry, had Kerry won the 2004 election, both of these decisions would have come out differently.
So whether you like these decisions or hate them, elections do matter.