Thank you for posting of your experience!
No need to apologize for the incomplete project. If you never fail, you aren't trying hard enough. As you reflect in your analysis, the exercise is good. There is no such thing as a wasted push-up.
I totally agree with the tendency for technical issues to overwhelm game design issues. I don't want to think how many hours I spent this week trying to fix key-repeat issues with libtcod.
My planning process:
1) Identify the core minimal product that would achieve my vision. You want this done as early as possible. When it is done; it is playtesting & refinement.
2) Identify riskiest tech stopping your minimal product, and address that first.
So if physics based path finding was a pre-req for your game design idea, you really did nothing wrong for planning. If the game design could have worked with crappy path finding? Then better planning would have focused on other tech first.
But I feel for your path finding pain. I was lucky my Smart Kobold systems got me pretty close; it was more about finding proper tie breaker rules than any base tech.