I know a guy who runs a what I would call successful sports card business, using all three venues (online, card shows and store front). He basically explained it to me that he uses card shows to sell items that are "hot" and of local interest. The Internet (Ebay) to sell things that are not quite so popular in his local area. And the store front was basically for buying cards, especially larger collections and vintage.
He also claims a yellow page add is worth its price right now because as older people (who are often times not too Internet savy) are looking to sell cards they have been hoarding for many years they tend to use the traditional methds.
I only see him three (maybe four times) a year at local shows, but judging by how quickly his vintage singles turn over, that model must be working. It seems like everytime I wipe out a huge section on my wantllist of whatever vintage set I'm working. In two months I see him again and he has more.
Hope this helps,
Marvin