Or else another idea is to come up with nbb native anti spam :
Drop a cookie every time a page is loaded via browser, if someone tries to comment without the cookie being dropped in the browser! Its probably not human and the comment can be moved to a moderation queue. Whether it be comment or new topic.
Second, if a user is making more than 3 new topic every minute, the fourth topic need to not be allowed to create without a cool down period of 30 minutes. This is used by reddit.
Third, there are many servers like stopspam and all which stores a list of the most spamming IP addresses, so nbb can check an IP against their database before allowing an IP to post more than 5 topics per hour, but a person with more than 3 reputation points can be avoided these checks.
This way, u don't need to have akismey or spots without honeys or captcha, if user wants additional protection, they will install plugins.