Excellent points Dana and I think you're absolutely partially correct. I strongly agree that there are a "whole lotta things all working together" that need to all be addressed. For sure!
As for the "how big of a deal is this redirect" discussion, I think it depends and differs case-by-case.
I also discovered this issue at the company I'm currently working at when I started there 8 months ago. I also discovered a ton of other weird issues related (like 2 index pages.. !?!?!) that I literally had to argue with the engineers over for days.. (They honestly believed we needed an index.htm and index.html page with identical content.. I think they still do even. ugh)
Anyway I FINALLY got them all redirected and we absolutely saw improvement. (Also, going from PR3 to PR4 is a big deal!! I'd throw a party for a PR bump!) We saw improvement in almost every one of our target keywords.
Here's why I think our cases differ: It all depends how the links were built prior. Meaning if you have links built to domain.com and to www.domain.com equally, the juice will be split between them and when that redirect happens your main domain will get a bump. This is what happened in our case and I knew it would going into it as I did a nice long scouring of our link profile prior.
So I'm guessing in your case they had all correctly built/gained links to the same version of the domain keeping it from being split.
Still it is my experience that when you get a link some people go domain.com and some go www.domain.com and in this case if the two are different you will definitely lose out on some great juice.
Nonetheless Dana, you are absolutely right that there is no end-all be-all in this business. (That's why we all love it so much, right?!) And it's also why I tried to stress that this person go through your list as well as heed my advice. Your list is much more thorough and a great launching pad for anyone looking into a similar issue.
Onwards!