Working out if they are nofollowed or not probably is comparable effort to just posting the spam link! Therefore just posting the spam link is probably the best strategy for them.

For one link, yes, but for the entire site? I wonder.

I can't imagine there are any search engines important enough to optimize for that don't use the rel=nofollow cue.

Source: http://www.socialseo.com/blog/an-experiment-nofollow-links-d...

Google "nofollow seo value" to find other insights.