If non-admins had the ability to "flag as spam" it might be easier to sort through at the very least.
This would not be useful. I'm using the forum's RSS feed so my PC makes the sound of truck when someone posts and i'm like YAAY SPAMS TO BAN.
I've also seen forums where, before creating a thread, you need to answer a simple question related to said forums. As an example, we could use: "What is the name of the protagonist?".
This was exactly what used to be there all the time, since ~2011, when the first big spam wave started.
Other than that, I don't see how it can be limited.
Seems that they moved hosts, as some subdirs that were on the server are no longer there, the forum member list is back (it was an empty page before), and the forum's version number jumped from 1.1.17 to 1.1.19. So apparently whatever spam protection was there got lost during the move.
That said, the questions require to register were a bad choice imho.
I know of enough people who were initially unable to register because they were not able to spell "independent" right, apparently.
I had sent a nice SMF registration antispam plugin to derek back in the days but apparently it wasn't good enough or dunno.
I'm also worried about the wordpress version used for the blog. It's kinda old, and the exploit list available is quite long.
yeah, me too... No idea what to do, though...
Mmm.. Try to use an exploit to get in, and apply some extra security this way?

If i had the chance i'd certainly patch the thing for good.
But no, better not this way.