I've always thought Keyes was an incredibly eloquent speaker -- when I first heard him, my thought was that American political discourse had not had such a speaker for at least 50 years previous.
What I've noticed since then, is that often when I hear him speak, my first thought is "That was beautiful!" followed by "but what did he really say?" I've especially noticed this in trying to condense what is being said to transcribe it on the AKIMS live threads.
In fact, I'd encourage people who disagree with what I've said to go back and read the Transcript of Alan Keyes CPAC Interview. You'll notice that Dr. Keyes has a wonderful vocabulary, but in many sentences, he gets caught up in the verbage and never finishes his thoughts. In others, he uses 20 words to say what he could have said in 5.
Playing to an receptive audience does this over the years. But, as you mention, those who were delighted at first drifted away as Alan became a parody of himself.