Our U.S. Senate is the most self-important, megalomaniacal confederation of mediocrities known to man, as it is.
The idea of further insulating these men and women from public scrutinity-which was in part responsible for their increasingly negative reaction towards the Miers nomination-is preposterous, in my opinion.
Your assumption that similar personalities would be elected by state legislatures is questionable. Many, if not most, of those seeking senate seats today have narcissitic peronalities and would not fare well with state legislatures looking for team players.
Checks and balances were not just for the three branches of the Federal government. It's my understanding that Senators were intended to be essentially ambassadors for the separate state to the Federal government. Allowing the state legislature to select the Senators placed more power at the State level. In part because of the 17th amendment, Federal government becomes more powerful while State goverment becomes less so relatively speaking. The selection of Senators was the main check against encroachment on the States by the Feds. State governments are becoming not much more than extensions of the Federal government. I don't what the pre-17th situation was or if it had the effect its proponents expected.