The nature of discussion is that the topic will gradually evolves and changes, however I do agree that a lot of the long runing topics have gone very much into general discussion and jokes.
I will hold my hand up and say YES, I am as guilty as the next person with that. But when something starts up that catches peoples funnybones it does tend to snowball.
However if a topic is still relatively serious and still on a Star Wars line then I personally don't believe it should be closed, unless of course the topic is duplicating somewhere else.
As for the number of posts ina topic, 100 is a good number I think and it's at the discression of the Admins/Mods if they wish to let it go over.
One thing to remember, this is no longer really just a discussion forum, it has developped into a samll community of individuals who are getting to know eack other, forming online frieddships and enjoying a sence on comradery on the internet.
Just my thoughts on the subject.