I have been using my D40 with 18-55mm kit lens for four years now and love it to no end. Two and a half years ago I fell down face front in a steep beach slope while I was wearing the D40 around my neck and loads of sand got lodged in the lens. At the time I had difficulties while zooming in and out, and the auto-focusing wouldn't just work. After a while, zoom and the focus started working normally.
In the last year or so, I have noticed that the auto-focus would stop working for brief periods of time. Of late the auto-focus has stopped working altogether. Whenever I try to auto-focus, I can hear the motor try and fail. So I have started to adjust to the manual focus and am started getting the hang of it.
I am also considering buying a tripod and the wireless remote. I understand the core concepts of photography, but I have only used the camera in a hobbyist way and not to produce seriously good pictures.
How can I make the best of use of my D40? Would D40 be useful to get some great shots that I could potentially use for a portfolio?