This thread is one of my favorite topics on the board, and to be honest, I think speculation is one the things that makes it fun in the first place. I don't really see how, or why you would seperate them. What would a rumour be without speculation and vice versa? Wouldn't it be a sort of forced to post the rumour in one thread, and than start talking about it in another? And what is a rumour to begin with?
I am not a native english speaker, so I might be wrong, but I think a rumour is an ongoin story that might be true or not true. Something people talk about (ok I admit I googled it) so in essence I feel a rumour is basically something that is ongoing, information in transit. it is moving, not a static fact. As such, I think, talking and speculating of what posted information could mean is not different from a rumour, it is part of the rumour, it defines the rumour for what it is.
just as an example: The weekly rumour engine. The posted picture is not a rumour...it is what people think they can make out of it it and the speculation that follows that makes the rumour. Thats why it is called an engine, it starts the rumour. Some people believe what is said about it, others don't . Sometimes One provides good arguments, sometimes It is close to wishlisting. But as long as there is some reasoning behind it, I really don't see why it would be off topic in a rumour thread.
sure, it happens more then once than things evolve into discussions that end up way off topic. But up to us, or a mod to signal it and put it to an end after some time.
just my 2 cents