I think that in some ways the rise of spirituality in Judaism came about as the practice of the commandments became more symbolic. The Orthodox say that Torah encompasses everything in the universe, and I believe that this cannot be argued against, at least not for the ancient Israelites. There was no concept of religion. The Torah described what to do in all aspects of life. And since the Israelites were their own nation, many of the commandments also defined how the nation behaved. There may have been individual Jews that were not performing all the commandments, but as a nation, the Torah was a document that was laying out a blueprint for the behavior of the nation.
For whatever reason, whether it is was a commandment of G-d (as the religious believe) or whether it was a custom or superstition(as the atheists believe), the Jews only ate kosher animals. It was the way of the nation, just like compulsory education is something we have in this country. There was no need to imbue it with "spirituality".
As the centuries went by, I think several things happened. The first is that for whatever reason many of these customs were forgotten or not in practice by the majority of the populace. In many ways, it was the Chazal who reinstituted these customs and I think they had to add a little umph to these practices that were no longer "just how things are done". When I read the works and stories about these proto-rabbis I get the sense that they were the first group to say that just performing the commandments is not good enough, in contrast to the Sadducees, for example.
The other thing that happened is that Judaism had to contend with its rival Christianity in most places where Jews lived. Christianity set itself up as the religion where spirituality is a lot more important. As a matter of fact, i think the focus on mitzvos is one of the key faults that the Christians found in Judaism. Partially to address the spiritual needs of the Jews and partially to compete with Christianity, there was a lot of spirituality added to Judaism during the age of Judah the Chassid and the Kabbalists of Provence and Spain.
So this is my comment on Tobie's post. Mostly my opinion, but hopefully based on reasonable statements.