While Abraham had become materially rich in his travelling, he still considered all his worldly goods useless. In Gen. 15:2-3, Abraham asks the lord "O Sovereign LORD, what can you give me since I remain childless and the one who will inherit my estate is Eliezer of Damascus?... You have given me no children; so a servant in my household will be my heir." (NIV translation)
Then, as now, the wealthy want their estates to pass to their children, not their underlings. Would Abraham have given up his estates to have a child? Perhaps, perhaps not. But he considered a child (read: a son) the most precious gift God could give him.