I am curious if lesser (everything minus head or maybe lower manifold) gaskets be reused upon engine reassembly, if they look in a good shape. In my particular case, I took one (of the two, V6) valve covers off, which affected the upper manifold (AKA manifold-intake) in addition to the valve cover gasket. They are both detachable rubber gaskets and they look in a good shape. The replacement is cheap (<$10 each) but I have to wait for delivery.
I reused cork rocker cover gaskets many more than ten times with no problem. I used sealant to glue them to the covers so they came off with the covers and were not damaged. I am not recommending this action. There were extenuating circumstances; 1- I was poor, 2-they were thick cast magnesium after market covers, 3- I seemed to pull the covers often to adjust valve clearance or something. As previously noted , the most likely cause of leaking valve cover gaskets is overtightening , by other than the manufacturer.