Yes, I think the engagement over a prolonged period of time is key. Also, combining to your Twitter feed is a good idea. Like with other outlets, ( think of TV ) posting it is best to post at different times during the day to reach people you otherwise wouldn't. Posts often get lost in the shuffle and by posting during different times, you reach a different audience. I also wouldn't be afraid to post multiple times during the day. Sure, some people may be irritated with your constant posting, so it does come at a risk. But, ask yourself this, what do the large companies do to us on TV everyday? Yes, it's annoying but it does work!
Another thing that I am toying with doing when I launch my kickstarter project, is to send direct messages to people on Facebook. This, of course can be time-consuming, because you would need to do send the message to each individual person. My thought process is that people respond well to direct messaging. If I ask them each to share the message on their Facebook wall at a specific time, I think it can reach a lot of people, all at once. This is just a plan I am thinking about doing but I think it could be beneficial. If anyone has tried this, has any tips for doing this efficiently or reasons why they don't think it will work effectively, please let me know