With grid state initially off I could get what I really wanted with "g" toggling after setting in backend_bases.py event.inaxes.grid(which='majorminor)
It does exactly what it supposed to do -toggle visible grids. See my figure for a clearer description: http://img249.imageshack.us/img249/1464/gridimage.png
The top-left figure has major-minor grids enabled in log-log view. This creates not a pretty image --neither on screen nor when I save the image as png or pdf. Top-right is clear since it is spaced linearly. The last figure I toggled with "g" key. It was originally like the first figure on the screen. I realize also that grid accept alpha keyword, however I couldn't get a satisfying result out of that either. For the time being I will go with full-off grids for my step plots.
With this said, I still think event.inaxes.grid(which='majorminor) should be checked-in since it is the right behavior for full grid toggling. That's what toggling is about right? Either all or none --we don't want gray areas.