Keeps have ten levels of potential upgradeability. When you upgrade a keep in New Frontiers, you will visually see the geometry of the keep change. The footprint is not affected, but upgrading will result in taller towers, taller walls, and more hookpoints for siege weapons and NPCs. For more detailed information on upgrade fees, times and NPCs, please see the New Frontiers: Keeps page: http://www.camelotherald.com/article.php?id=86