fostering rescue dogs is where you invest your free time in. it's a worthwhile use of your time, and you probably wouldn't do it if you didn't get something out of it.
then why do you do it? (i don't mean to criticize your choice, but i am curious, and i wonder if we can discover a motivation or reward that you haven't considered. i certainly believe that you are doing something good, so i wonder why you feel you get nothing out of it)
edit: i just thought about this some more and i realized that there are plenty of situations that could have brought you to where you are. i don't want to speculate what though.