The team manager at work likes to bring up the list of "time investments which we will benefit from later" which we never benefited from later. It's a good point that usually its better to wait until the benefits are obvious rather than predicting at some point there will be some benefit later.

My general strategy - usually applied on a much smaller scale - was the first time I needed to do something similar (or the same) I'd copy the code. The second time, I'd consider abstracting it. By that time I had three applications and could better identify what was common and what was specific to a particular usage. I wonder if something like that can be applied to larger libraries.

That is what I tend to do as well. Heard it being called AHA programming. Avoid hasty abstractions.