Almost anywhere is "worth doing" from some point of view. In Normal mode you can get decent items like Magefist, Frostburn, Goldwrap, etc. Even Lenymo, the unique sash, is a pretty OK item if you upgrade it once or twice.
From a pure profit point of view, you'd probably be better off doing other areas instead, but there are definitely some nice things that can be found in Nightmare Chaos Sanctuary. Some examples are, Herald of Zakarum, runes up to Vex, Skullder's Ire, Stone of Jordan, Bul-Kathos' Wedding Band, etc. But you're not going to find a lot of those things given the amount of time you put in.
As far as skill charms specifically, you're actually best off in even lower level areas. The closer you can get to level 50 monsters, the better you'll do, because you eliminate some of the higher level (but less useful) affixes from contention, which increases the chances of getting a skiller. Nightmare Council and Nightmare cows are good spots, because they have fairly high chances of dropping charms.
Edit: Changed the required item level for skill charms from 42 to 50.