For me cabin dryness is mostly non-issue.
My throat does get drier if I speak more (or have my mouth open for a long time when I fall asleep head down), but that can fixed by drinking some water.
The only issue for me is for long-hauls I need to remove my contacts during the flight or else my eyes become really dry.
So think the best way is to get better moisturizer and lip balm, combined with drinking more water if dryness is a problem for you.
As for your second question, I have no feedback as I've never flown on the 787.