More importantly, the sheer volume of content (however mindnumbing) does boost the sites ranking on search engines.
Total page impressions are usually ~5x page impressions from logged in users. But the unanswerable question is how much of that traffic is driven by searches would reduce.
With this being the case, then I can't imagine it would be that hurtful to get rid of the mind numbing amount of meaningless content. Our lurkers are more valuable than our spammers, so if we can even transform any amount of the latter to the former then we'll be in better shape. I'm skeptical that our traffic driven by searches would be harmed, because I'd be willing to bet that the only searches these spammers are driving is airdrops and ICOs. The quality searches, that will drive creative, intelligent and long-term users that are coming for the right reasons are going to be searches that will remain at the top of search engines regardless. I don't think this site has any significant competition, but I might just be naive.
The last round of advertising pulled in 2.4
BTC https://bitcointalk.org/index.php?topic=3006864.20It is an auction and it is really a matter of opinion/speculation as to how that would be affected by reducing spam. Would the bidders pay less if there was less traffic?
I would argue that they shouldn't pay less, because the quality of traffic would go up at
least proportionately to the amount of spam that's reduced. Speculation and opinion as you say though, until something is done with tangible results.
Back to the closing threads issue. I don't think it would reduce spam as new threads will simply replace them. Many of these threads are actually opened by account farmers for the purpose of answering from their alts. What it would do is stop annoying anyone that replied early in the thread from constantly seeing them pop up in their unread replies page.
Would this not also fall under the opinion and speculation category? I haven't seen much evidence for this, at least in the thread I reply it seems that OP is genuinely interested in getting an answer most of the time, but then get lazy about locking the topic or simply unwatch the thread and never come back. I've been proven ignorant on many things though, so I'm not saying you're wrong; it just seems ironic to place the one as speculation and not this.
Your thought was good but in some point, have you consider the satisfaction of an OP?
The OP of a random thread is capable of unlocking the thread, so if they're not satisfied they can continue their search. Mistakes are not costly in this scenario.