How can a researcher improve his contribution to society?
On a different note from some of the other answers, try to take to heart that basic research is directly useful to society. Almost all modern pharmacology is based on decades of fundamental biochemistry and biology research. Materials science is based on years of basic chemistry and physics research. Basic math research fuels advances in all types of engineering, from signal processing to computational work to structural engineering. There are many other examples for other fields of research; please edit this answer or put them in the comments. 

In short, don't underestimate your current value to society.