The militia is not a military entity from my understanding. It appears to be more of a simple social grouping for the sake of recognizing one's roots. I would recommend that all who consider themselves Wessex would join LSV simply on principle. However, there's absolutely no perceivable harm in not being the militia so I leave it as a suggestion (it is also not my decision).
Having more numbers in LSV would allow us more leverage, but I am not all too familiar with the inter-alliance functionings and am merely speculating.
I would like to add that having that huge number on mumble only bolsters our own will to play. There are always people talking and waiting around to enjoy the game with.