Mavericks Internet Sharing over Ethernet stopped working
Okay, so I got it to work again. I had to manually enter the correct DHCP, IPv4, and DNS settings on the MacBook Pro.

Here are the settings I used to get it to work in Network Preferences on the MacBook Pro:





I had previously tried to do this manually, but I only tried the IP address stuff, I didn't think about entering in the DNS server until I read this article: http://forums.beyond.ca/showthread/t-216916.html

It's dumb that I have to do this manually now, and that I still am unable to see AirPlay/AirPort devices.