No, if there is already a thread of the model no need to create another one (unless it's to split content, like XXX thread and OF thread for pornstars), people who are watching the request thread wouldn't know about your new thread.
If there are 2 threads for the same content they are merged
If a request thread has enough content (e.g. 2 pages) it can be moved to the appropriate category, to do so report the thread and ask for it to be moved