I think when people talk about substance they really have other problems with the candidate but that sounds more sophisticated than "his name sounds funny" or "but he's a mooselim."
Look at Kerry last year. Few candidates ever have had as much substance and specifics in his speeches and people constantly complained he was boring people. It's not hard to find candidates actual proposals if you care in the age of the internet. Most people don't really care though. "No substance" is a crutch that gives you a convenient reason for not liking someone because frankly nobody talks "substance".