Personally I think it's better to revive an old thread rather then start a new one about the same thing. The one exception (for me at least) is if the opening is really bad. For example if the topic is about whether not you prefer shorts or pants and the thread opening is along the lines of "OMG PaNts be Th3 GreAT3st!!!" with no poll, I would be really tempted to start my own thread about it. The thread would have to be rather unpopular and at least 16 pages back before I would though.