I must say, that "under appreciated" is not such an interesting concept when it comes to the watches one owns. The question has to be asked: by whom? As long as the answer is not "by oneself" there is no problem.
Without it being my goal to buy under appreciated watches, I have the feeling that I quite often like watches that other people don't find interesting or beautiful. But so what? It is me who has to better like my watches, and I do. Having under appreciated watches make them more seldomly seen in the wild than for instance the iconic Big Pilot, but even that isn't too interesting to me.
Here you see two of my under appreciated pilot's watches.
The Worldtimer, the best one for its money, I am sure. Discontinued now, my advice: get one as long as you can.

The Vintage Collection Pilot's Watch, with its beautifully ribbed bezel: it looks amazing on the wrist.

Kind regards,
Paul