How many times printed printer can print it-self?
The files used to print these objects are digital, and do not degrade in any way after each printing. There are no side effects or degradation that occurs over time due simply to printing them multiple times.

This is the RepRap philosophy, and the machines are actually designed with enough tolerance for printing and building mistakes that even if the print isn't perfect, it will not only work fine, but it can print a printer better than it was printed, with some care and attention to calibration.

The process still takes a lot of human intervention, in the way of building the new printer and properly calibrating it.  If there are errors in the printer or the prints it produces, they can almost always be attributed to the builder/calibrator/user, and not to the design or the fact it's the Nth generation of printer.