Depends on what you're expecting with upgrading to PRO. If you expect some dramatical changes, then it might not be worth. With the basic version you can connect to 3 Ultrapeers and with the Pro to 5. The max. number of hosts, depending on your internet speed, is 14 with pro and 10 with the basic AFAIK.
The $ 18.88 for the Pro, a sum you easily spend on a Friday night between 8-10 pm, is rather a kinda support for the developers of LW, so they can continue the further developments of the program necessary to keep the network as a whole up and running.
