I've suggested this in the past. I don't think it would be a bad thing if all new users are essentially shadowbanned until a mod has approved their post or account. It would at least get rid of bots pretty effectively.
You will lose them if it takes days to approve the post. In addition with spam replies, moderating posts and approving topic will be a huge pain for the moderators...
Why would we lose them? Waiting for a publishing approval is far the best option to get rid of newbie's repetitive/duplicated and/or trash posting. I've also saw recently that there are a lot of newbie topic makers in which is too cliche to ask, most likely on the Bitcoin Discussion board, Meta, and Beginner's and Help (pretty understandable). And if they are really skillful and motivated enough, why wouldn't they wait?
Maybe if a newbie post approval isn't acceptable by other users and the administration, I think it would be better if their post were limited by 500 characters. This isn't a hard thing to do especially if they really are browsing and trying to gain knowledge in the forum. In that case, they will be forced to make their post lengthy and with length comes ofcourse numerous ideas to be built. Though it's kinda harsh to the new comers, it would somehow strengthen the quality of the forum.