I would like to see us go back to appointing and recalling Senators. I really believe that that was the way the Senate was designed to function properly and ever since we tinkered with the founders wisdom, we have built this club for Specter and his ilk.
That was very easy for me to say. I have much more difficult time coming up with a workable plan to make it happen. Since these “Members” seem to govern themselves, it doesn’t seem likely they would agree to tear down their own clubhouse.
As an alternative (and a plan I actually like better):
Establish a 'vote of confidence' (for lack of a better term) process. At each major election (every two years, generally), voters vote for continuance or recall. Set the bar high enough that it can't happen lightly -- say, if the number of voters casting a vote for recall is equal to 2/3 of the votes cast in the previous election, then the senator is recalled.
Prevent re-entry. If a senator is recalled, he or she is barred from holding any elected office in their state, or from engaging in business which puts them in contact with elected representatives, for a period of at least ten years.
This ought to be possible at the state constitution level -- if it's an amendment, it would make it hard for state lawmakers to dilute it.
If we ever get to the point of calling a constitutional convention, that should be one of the main items for deliberation.