Today, I finally took some time to mend them. My stitching was rushed, and I'm all out of the original yarn for these (at least, I think I am), but I was less concerned with how it looked so much as whether I could keep wearing the mittens for at least two more months. I am thinking I will not need them often in April, but lasting through to May would be ideal (we get the odd late snowstorm, after all).
For the one with relatively minor wear, I just worked duplicate stitches over the existing ones.
For the one that was trying to fall apart, I had to get a bit more serious.
I wove the two colours through the area to reinforce it.
After that, I worked duplicate stitches, one colour at a time.
For the thumb, I just caught all the stitches that were in danger, and kinda whipstitched them into place, more or less.
It took awhile, pretty much all morning, but, it was still a lot faster than knitting new mittens, and I'm afraid that I don't have time to knit mittens for me at the moment. Too many other things to work on, but hands must stay warm in the meantime!