Wi-Fi Diagnostics app not found
In 10.8.3 and lower, the program Wi-Fi Diagnostics is the tool to measure RSSI, signal to noise ratio and to scan for hot spots (a.k.a. war driving). That app is gone on 10.8.4 and is replaced by Wireless Diagnostics that has many but not all the same functions. Bonjour scan is out for instance, but the scanning and measuring tools are far better in the new tool. 

The new application Wireless Diagnostics.app works mostly as the referenced article notes as well


  it is now more conveniently available by holding the Option key, clicking the Wi-Fi menu, and selecting Open Wi-Fi Diagnostics.


PS: As a side mark, you can't execute Cocoa applications from bash the way you tried. Use /System/Library/CoreServices/Wireless\ Diagnostics.app/Contents/MacOS/Wireless\ Diagnostics or open -a "Wireless Diagnostics instead.