Can’t see other Mac workstation via ethernet but OK over Wi-Fi

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:

1. Firewalls (OS X, Little Snitch type, malware, and/or internet firewall like Symantec and others)
2. 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.

It could be an duplex mismatch problem: small packets, like the ones ping sends, get through while large packets (as generated when browsing the web) get delayed or lost, which leads to poor performance.

This problem may arise either when the autonegotiation process between your Mac Mini and the Netgear minihub fails or when speed/duplex mode are set manually and don't match at both ends.

To solve the problem you first need to check the Ethernet settings:

• Open System Preferences>Network, select Ethernet from the list on the left and click Advanced....
• Select the Hardware tab.

Then:

1. If configure is set to "Automatically":

   

   autonegotiation is on. Change it to "Manually" and try different Speed and Duplex settings, for example:

   

   until the problem is gone. Note that you must press OK for the settings to take effect.

2. If configure is set to "Manually", change it to "Automatically" and test.

3. If nothing helps, try another hub or connect your Mac directly to the router. If that solves the problem replace your hub.