Hi Mark,
Don't see any similarity between the server window and the client window. But client window in standalone mode and networked mode are equal in my opinion (only configuration settings are different and that could be solved with showing a different dialog for example).
This thread has also several possibilities to handle similar GUIs (described also my approach).
So you could certainly have 2 (or 3) seperate screens which extend all from some parent class for example, Observer pattern is not a must requirement. I did it with 2 seperate screens (1 for server window and 1 for client window). So there is no difference in the client GUI between both modes, which looks very logical to me: no difference in functionality, only in configuration settings. So why creating 2 seperate screens...
Kind regards,
Roel