I am relatively ignorant about Thomas and so these comments are only tentative. I would like something more blatant to convince me, and I would like to see more agreement in order. Luke in his redaction of Mark's parables consistently makes them less allegorical, yet he is later than Mark. I have commented on this before on the list. Suffice to say here that I think the idea of a a steady, easily traced development from low allegory to high is a bit too simple.
Life is more complicated than that.
In which case, this cannot function as an argument for earliness. Thomas may of course have known the synoptics and still 'used' oral traditions independent of them in which case the discussion of 'scissors and paste' would not be so relevant. My own gut feeling would be that Thomas interacted with oral traditions, some of which had themselves had interacted with the synoptics. These are just tentative thoughts and comments of one searching for the truth on Thomas, much enlightened by Crosstalkers who continue to help on this.