first off, where do you get the 99% effective statistic? I'm genuinely curious, because I cannot think of a reason why the simple addition test is effective at all; i am still as baffled as ever.

as for hired spammers, i don't see a protection against that, nor do i challenge your argument about it, but the subject is CAPTCHAs. CAPTCHAs are turing tests; they tell computers from humans, not humans from humans. the difference is that botnets take very little money to run, once the software is mature. hiring takes money, and that in itself is a barrier. i don't know the true costs of running botnets vs hiring commenters; perhaps as you said, hiring is more cost-efficient, but it seems almost trivially easy to defeat the "2 + 3" mechanism, so trivial, that i would assume it to cost significantly less to defeat than hiring somebody even at 6 dollars per hour.

if the hired commenters post "intelligent" content, well then, it is, by definition, intelligent content. if "intelligent" only means "coherent" and "somewhat related to the topic of discussion," fine, it can be spam, but it still fits two criteria: 1. a human posted it, 2. it required mental effort to create. a legitimate user who is a maniac wouldn't fare any better. as such, i would believe that a hired commenter who posts "intelligent content" is as at least as intelligent as a nonhired user who posts "unintelligent content."