If there IS philosophical progress, is it worthwhile to read philosophy that was
I agree with Ian for similar reasons (see my Unsolvable Problems and Philosophical Progress)
So, because we both agree that there is philosophical progress, is it worthwhile to read philosophy that was written before you were born?
Yes, for at least two reasons: First, of course, some of that philosophy might consist of good reasoning that has not been improved upon. Saying that philosophy progresses doesn't mean that old philosophy is "wrong" in any way (any more than saying that science progresses doesn't mean that old science is "wrong").
Second, philosophy is best thought of as a conversation that has been going on for at least 2500 years. One of the best ways of joining that conversation is to read "transcripts" of its earlier stages.