Not sure if this is any more useful to anyone, but since I did it, I figured I'd share it.
I tried to go through and apply the useful points of interest to the GPS tracks provided above. So far, I've just worked on the section through Manistee, referencing points of interest from the maps from MMBA's Trail Guide. For now, points of interest include access points, campgrounds, and water sources. Disclaimer: the water sources are simply transferred from the MMBA map; I have not verified any of them.
North of Manistee, the MMBA maps don't show anything, so it will take a little longer to go through and identify points of interest.
Google's map making program is a little quirky, but it works well for making, sharing, and collaborating on things.
North Country Trail - Lower Michigan