16GB is alot of space, and after 4 hours, i bet everyone is going to be at least a little irritated, and probably hungry or thirsty. 4 hours is a long time to be shooting continuously.
Also, 16GB is alot of pictures to sift through and edit. It's like what fiveoboy said, your post production is going to take you a few hours to do if you're going to give them all the pictures edited if you're going to do more than just assign color profiles.
Based on what's on your flickr page, i bet if you really do spend 4 hours shooting and finish with 16 GB, with each file being say...35MB, you're going to be spending at least 6 or 7 hours JUST EDITING about 468 pictures...
That equates to 78 images per hour, which means you're doing really rough, minimal editing, which means you're doing at least 10 hours of work for $30/hour.
For $300, I think as a photographer, and a client, everyone would rather you shoot say..100 pictures at most, spend about an hour or a little more shooting, spend time doing sound editing, and delivering quality images to them.
Quality over Quantity.
On Monday morning, i'm going to shoot some portraits for a friend who's graduating college. I'm going to be bringing some muffins, some water, i'll arrive an hour early to scout out some places, we'll hang out and talk a little, shoot for an hour, and if it's a good day, will deliver probably about 5-10 solid pictures of her. it will be pretty modest. But it's the concept of quality, which I know she'll be more appreciative of as opposed to this run-and-gun motor-drive for 4 hours and slap together some rinky-dink color adjustments across 500 pictures and give em a disk.
It's the Craigslist scenario:
I shoot your wedding for $200, all day, you get a disk a couple days later with all the pictures on it.
$50 I shoot senior portraits for an hour, at the end of the session, i give you the memory card so you can do whatever you want with the pictures.