In many ways, the role of the Senate is the Guardian of the Republic. It's original purpose was to provide to the States what the House of Representatives provided to the citizens: a direct voice and agent for their interests. However, that role has been substantively eroded by the 17th Amendment to the US Constitution, which has essentially given us two Houses. The impact of this has been a complete eradication of the conept of federalism - such that even supposed champions of states' rights, the Republicans, pay only lip service to the concept (witness only the Schiavo case for proof that federalism, like fiscal conservatism, is long since dead in GOP circles).
I've previously written about the corrupting influence the 17th Amendment has had upon our national political discourse. Briefly, it has become an avenue for special interests to dominate the Senate as they do the House. I reject the short-sighted arguments that repeal would lead in the short term to undesirable political outcomes; most conservatives are agnostic about the repeal, but liberals tend to say that repeal would give Republicans an advantage given that most state legislatures are GOP-dominated. But the short-term impact is not my concern. In fact, repeal of the 17th would lead to more independence from the "party above country" mentality that drives modern politics in this modern (and thoroughly Republicanist) age.
Glenn Reynolds just mentioned the idea of repeal, and poses an interesting counter-proposal. His suggestion is to make Senators ineligible for President, thus bluntig most of their aspirations and focusing the Senate on the business of being the Senate rather than a grand stage. However, I think that while it has some merit, it's a symptomatic approach, which would not address the underlying issue of who Senators are beholden to when they assume office. It's the quality, and motives, of the Senators before they arrive at the Capitol, not how they comport themselves after they arrive, which concerns me and why I still favor repeal. If repeal of the 17th were to come about, I think that Glenn's suggestion would be rendered largely moot.