Self-Assigned IP on Ethernet (en0)
This looks like a basic networking issue where you might need some knowledge to sniff the packets on en0 using tcpdump.

The things that are known to prevent DHCP from reaching the OS are:


Firewalls (OS X, Little Snitch type, malware, and/or internet firewall like Symantec and others)
Network setup where the DHCP server only sends addresses to machines that are cleared for the network


You seem to have done some of the easy troubleshooting, and I personally don't ever like deleting some plist but not all plist since there are many keychains, system plist, ByHost plist and others so you could actually make a problem partially deleting information on networking.

The one thing I would do is re-connect the known machine and record the IP address that gets assigned and swap in the "suspect" machine and force the IP to be the same. If you get network connectivity then you are on the right track with DHCP issues.