I don't see what makes geography so special. If a politician tried to "just campaign in New York," he would end up appealing to people outside of New York as well. A politician who took a liberal position to appeal to New Yorkers would appeal more to some hippy living in Montana more than a libertarian who lives in Queens. And anyway, in the world of mass-communication, all campaigns are national no matter where the politician actually goes. Even in the current system, a presidential candidate could spend the whole campaign season in an underground bunker and still get his message out the people, it's just that it would make for bad PR.
Admittingly, some issues are more intimately linked with geography. People who live in Texas have more of an interest in border control than people who live in Kansas. But there are many demographic issues like that. Men and women have different interests, young people have different interests from old people, Christians have different interests from atheists. Computer programmers have different interests from factory workers. We do not skew the voting system so that any of these demographics are more evenly represented, so what makes geography so special? (Besides the historical reasons.)
Of course, I suppose there might be a certain benefit in trying to give geography a more even representation so as to encourage that states maintain their fair share of the whole federalism game, but that really seems like what the Senate is supposed to be for.