Originally, the cards were meant to be folded (hence the name), so a seperated card is viewed as trimmed or altered. While they do have some value in the hobby, it is minimal compared to a complete card. The Cobb and Mathewson end panels sell for the most. As mentioned, SGC will not grade them. They are still a cool collector's item, and would still be enjoyable to view in their current form. A thread on this subject existed some time ago, and may offer a little more info...
Link to older thread