I think in general, most people don't even know how to play their cards. They definitely don't have any idea how stack size influences proper play. So the big variance in stack sizes (buying in for both 20x and 200x the BB is common) is just another source of bad players' mistakes, and something else for a good player to take advantage of.

Buy in for whatever you're comfortable with.

I always like to buy in for $50 at those tables, just to have a normal stack at first. This is partly because it's what I'm comfortable with, and partly because I prefer NOT to get on people's radar as a good player, when possible. I can double up to $100 and people who arrive later will just think I bought in for that much.

Even with a $50 stack, I usually cover all of the table except for 1-2 players.