Do you think the Bible and Quran are spiritual guides for spiritual beginners? Should folks with a more advanced spirituality move on to something else? Are those two scriptures kind of the spiritual equivalent of training wheels on a bicycle? Why or why not?
I will address the Hebrew bible (OT).
There is a large movement of studying the bible as a human work and not as an absolute 'spiritual guide'. I am rather surprised by the OP, im surprised that an 'advanced spiritual' person will have nothing to enjoy in the bible. the bible has earned its place in human society through the centuries, it has inspired our best artists and musicians through the centuries, Salvador Dali, Michael Angelo, Leonard Cohen, I could be wrong, but I believe that these people were/are sensitive and intelligent, or 'spiritually advanced' if you will.
the bible has brilliant texts such as Ecclesiastes, Song of Songs, Psalms. it is in fact much more than a 'spiritual guide', it is a window into a cultural treasure wich has inspired not only highly tasteful individuals but whole nations and Empires.
as a secular man, I believe we only shoot ourselves in the foot, if we think we need to 'move on' from knowing the work that has inspired western (and eastern) civilizations for centuries. the true beauty of the bible is revealed when we do not look at it as 'the word of God', but as a brilliant, emotional, and educating work of human beings, who lived in what may have been a difficult reality, but also of the most fascinating periods in history. when outstanding empires competed over dominating the old world of the day (the ANE).