Why is the site in beta? Is the beta programming related (i.e. the back end platfrom of the website and the UI), or is it more related to populatrity and interest (i.e. is it waiting for a certain number of members)? I would like to see this site become a full-fledged stackexchange website, so is there anything that us members can do to help it come to fruition?
All Stack Exchange sites start out as proposals on Area 51. This site was in proposal state there for over a year. When a site finally collects enough interested users, it moves to Private Beta state, where only users who signed up for the proposal can operate. The site later goes into full Beta, where anyone can contribute. At this point, moderators are also elected. While the site is in Beta, its status and maturity are still monitored on Area 51. Signal Processing is not an exception. When the Stack Exchange and Area 51 decide that the site has matured and is steadily growing, it graduates to the status of a full site. We're not at that stage just yet, but we're making steady progress in that direction.
What members can contribute are good question and good answers. We're also planning some community events like tag editing, question clean-ups and so on. There are coming very soon.