Don't get me wrong, having a hurdle to sign up is a good idea. You will get more invested members that way, and less spam. But you can choose different hurdles that don't exclude people who aren't well-networked. For example, you could require every new user to fill out their profile with detailed answers to questions, before allowing them to post on the forums.
What is else left for us to do in this day and age to minimise spam and abuse?
I know this because I personally saw a couple of spammers openly talking to each other about giving each other backlinks too.
I never thought that spamming like that would be worth the time or effort, but apparently it was.
https://news.ycombinator.com/threads?id=dileepand06
It is quite unfortunate I can't just mark an obvious spam and get rid of it.
I wonder how much value these guys get from posting spam links on HN.
As for spam ... I've not noticed it. I got bored of other people's boast-posts early on and now mark them as read before opening them.