Yes it is worth it to sell items from Normal mode if you find the right items. I have made a couple million gold off of selling items in the range of level 1-40. Do searches on the AH with the type of stats you're seeing on item drops and start looking over the items that come up and their value. If you do it enough, you'll learn which stats are desirable (even for classes other than your own), and which are not. Then you'll be able to sell the crap items to merchants to make space to pick up the good stuff to sell in the AH.