Not sure there's a formal downside to spray foaming them. I would have done that myself but couldn't afford it.
Amen - tripping over a bag of $$$ would have brought it all down to a phone call, like so many other projects - but necessity is the mother of invention. Saturday's outside temp here (also in Ontario) - a balmy -34 deg. A good day to find any spots I missed I suppose. Wood stove heat - and overall the (unheated) crawl space has stayed above 46 deg. I suspect this would have been a big freezer without the insulation at the rim. No regrets.