I'm totally with Dan on this. I've been reading through both the Sketchucation and the Sketchup Forums for a long time. (And many other unrelated forums). There have been so many threads I've encountered that span over years, and there's nothing wrong with them. When searching through the (not so friendly) google groups, or going through apple support groups for example, there is nothing more frustrating than to reach a thread about a burning relevant question, only to find that the thread is closed to further comments... almost answering the burning question, but Not Quite (or not at all)!
A simple reply is all one asks for, but then... no! Thread closed.
Then one must spend an hour (or more) reviving the essence of that thread into a new thread, confusing one self, and all the following searchers / readers who will find themselves bouncing between multiple threads in search of an answer to their questions.
Auto closing a thread sounds wrong to me. Maybe close threads that have been marked as 100% answered or something like that. And even that doesn't mean they are ever 100% answered. There will always be someone with a relevant question that doesn't necessarily require a new thread.
Keep it up to the Forum mangers, Sketchup Sages, or what ever Label the "Gods of Forums" use, to decide if something is off topic, irrelevant etc... have stricter rules for posting or something like that... if that's the problem...