Traffic definitely! ...however it doesn't mean automatic conversion to signups or activity. It's definitely worth it in my opinion to utilize the space for advertising if the community allows it. If your content is useful/entertaining and you bring value to their community I find that practice definitely attracts potential members.
Kind of. I just have "proud owner and founder of website name since insert year and date the site was first available to public members" a lot of it depends on how active you are on the other forum and the kind of traffic the forum has in general.