By all means, toss it on the compost pile. The humus in the old potting soil has completely decomposed and needs to be replaced. You can simply mix some compost into it, if you have some around. It might help to mix in some perlite, as well.
Tossing the old soil on the compost pile, however, helps to cleanse it of disease-causing organisms, without actually sterilizing it.
"Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?" - Douglas Adams