They aren't "essential" or "necessary", but they do help us get a feel for what "In the fullness of time" means, and that has value. But yes, they don't appear to be divine inspiration, and I kinda feel that is a shame.
On a slightly side note (but still on topic), are you familiar with the Epistle to the Church at Laotecia? It's mentioned in Colossians, and I have the text of it at home. I couldn't find anything in it that wasn't proper. Actually, it reads like a short version of Colossians, sharing many of the same phrases. I just wondered why it wasn't considered for canon. Not that it really adds anything useful, but just because it is actually mentioned, and it's Pauline.
Now there is something you will not find in everyone's library.
It is my understanding that there were no doctrinal changes or statements that are not found in the other writings of Paul.