CPU: Speed is nice, to process possible lot of data. many cores is less relevant since processing is serial by nature.
Memory: By default Wireshark tries to do a lot of analysis, gobbling up memory, so for larger captures more memory is better.
Disk Speed is nice, to be able to keep up with fast networks, if that's your thing. Also size depends on you capture needs.
Interfaces: pending on your capture needs, a fast interface is nice. Ethernet should be no problem, though USB-Ethernet may be hit or miss. A good wireless capture interface, with capable driver to capture with maybe somewhat hard to find.
