i "camped" at the bivi area the first time i drove to smith. it was dark, i'd never been there before (didn't know about the grasslands), and i was tired. i dragged my sleeping bag and pad somewhere there was an open spot, slept, got up early and got outta there. almost didn't make it though - they definitely make the rounds. (after that, i've pretty much always gone to the grasslands.) i've used the showers at the "real" campground a number of times and never got hassled.
if you've never been to smith and drive in a night, it's a pretty cool experience to wake up and see it for the first time as your own morning fog wears off ...