I cannot really comment on the earlier versions of the EK only that I think just based on the award numbers of the EK2 in the First World War it lost some of its initial grandeur. This happened again in the Second World War were the EK2 at the end was given to kids. Who doesn't remember the terrible pictures of Hitler awarding the EK2 to HJ boys in the ruins of his chancellery?
Despite the other awards Chris mentioned (some of them were proficiency badges and combat award badges, not bravery decorations), the EK1 had still a very high value. One could not be awarded the German Cross in Gold (the second highest bravery award) without the EK1 and EK2 ( or the Spangen thereof). Even the Close Combat Clasp was not tied to individual acts of bravery (like the RK or the GC) but rather to the accumulation of close combat days (which certainly required a lot of bravery, I know that!).
The Knights Cross of 1939 is a perfect example of the transition (maybe even degeneration) from an extremely high award to a more common award. The Knights Cross was still a very high award at the end of the war, but one should not forget that it was also a propaganda tool. The addition of the higher grades (which were basically second, third and fourth awards of the Knights Cross itself) is another indication of the inflationary tendency.
A simple graph which I included in my book makes clear what I mean. At the end of 1941, after the attack on the SU and after the battle for Moskau only 11% of all Knights Crosses were awarded. One can hardly say that the time frame between the Polish campaign and this date was not filled with fewer deeds of bravery then the timeframe after 1941. Another very telling point is that 50% percentille of all Knights Crosses awarded was December 1943! Meaning that in the last 17 months of the war as much RKs were awarded as in the 52 months before.
I think that this is a clear indication of a transition of a highly coveted and rare bravery award to one that was more and more used as a motivational tool - just like the EK2 was awarded in far greater numbers towards the end. It is unfortunate that such a graph cannot be constructed for the EK1 or EK2 due to reliable data. But I am sure it is similar if not more dramatic! (As a side note: the 50 percentile for the Oaks and for the Swords is March 1944 resp. July 1944 - supporting the above data and notion)
Certainly I do not think that the German soldier was either less brave in the first 52 months of the war nor was he more audacious in the last 17 month. Fact is, that Hitler himself approved every RK personally and that it was his decision to award more after the Invasion of Normandy and the Battles in the East. He certainly knew the motivational value of a Knights Cross or higher grade and that of an EK2 to a little boy he was shamelessly sending into the lost Battle for Berlin.
Dietrich