In my eyes, it's all about casting a wide net at card shows. A few years ago, I could walk into a show like Robert Morris looking specifically for my Pirates collection, and be pretty confident that I would walk home with a few hundred new cards. My needs were all over the place - I only had a handful of vintage, still needed more common sets like 1971 and '72. I even had holes in sets like 1991 Score or 1994 Topps. It was a safe bet that when flipping through a box, there was at least a 50% chance any Pirate card I came across would be one I needed.
And seeing all the great stuff everyone on the blogs comes across certainly hasn't dissuaded me from widening my collecting interests. So at the end of the day, I came home with about 300 new Pirate cards, a ton of new Steelers, a couple hundred Penguins, and then...a gigantic pile of random stuff.
I love adding new cards. And sites like COMC and Justcommons have made that easier than ever in the past few years. But for my money, nothing can beat a show. First off, only by flipping through random, unsorted boxes would I have ever stumbled across these cards. Nothing about my online card shopping would send me looking for Cliff Robinson or Cade McNown cards, but those two additions are two of my favorite pickups from the entire weekend. Secondly, while I gladly added the cards for a dime each, the cheapest copies of those two cards on COMC would run me a total of about $3. They're awesome. They are. But never in a million years would I have paid even half that for them. They just aren't worth that much to me. But at a card show? All things are possible.