An idea, not sure how easy it would be to implement.
Add a "button" on the first post of a thread named "SPAM".
Anyone seeing a spam post just clicks on the spam button, and the post is automatically moved to the spam thread to be reviewed by a moderator.
If it is spam, no one else will see it and it get deleted and the poster gets their account deleted.
Sadly, this won't prevent them from coming back, but this "could" keep them from doing anything else.
If it is not spam, then it can be restored to it's original location.
It's seems the recaptcha isn't stopping them.

I think this is a good idea. I also saw some spam earlier.

A button at the top of the thread or on every post?
Assuming it's not spam and no moderator is available, maybe an important post disappears into nirvana. And there are specialists who would then click SPAM on every post.

I found Spam in the Quest forum. mannatarora is their username.

I don't think dino run should be sharing links like that! http://textadventures.co.uk/forum/quest/topic/5whv3ppaiuqwafyw8hv8fw/take-all-form-containers

More spam.
http://textadventures.co.uk/forum/quest/topic/6cumphumiewhu4pv0wxgcg/how-to-get-decimal-wait-values

Petejohnee1 has spam for days.
http://textadventures.co.uk/forum/quest/topic/6cumphumiewhu4pv0wxgcg/how-to-get-decimal-wait-values

thanx, deleted!

Crackside is making spam.
http://textadventures.co.uk/forum/quest/topic/gfhg-wi8mkcom5p6m4wr7g/removing-one-object-during-a-foreach-loop