Finding comments closed tends to create a somewhat 'adversarial', vaguely 'hostile' atmosphere for some visitors. It's not desirable, certainly, in & of itself.

I frequently read old Posts, even seriously old. I am reading posts 4-6 yo, routinely, and posts that have been up a decade are by not means unknown. I don't often comment on them myself, but I do often see others who have and are currently 'chiming in'.

Sometimes, due to context, someone comes back to 'late' commenters, saying; 'Hey, the post is 2 (6) years old! It's all done & over!'. Then you get a little round of 'omg!' and 'lol!'.

WordPress' problem with comment-spam is WordPress' problem. They own it, really. For the WordPress world to be all hands-on-hips & glaring & huffing & puffing about spam ... hey, WP bought the model, built their whole gig around an obviously spam-vulnerable scheme ... so really, WordPress (and those who jump on the bandwagon & buy into WP) need to kinda suck it up & go with the fact that this is the price of the game they chose to play ... and not be pushing it off onto visitors to carry the burden & pay the price.

Making the priority the Admin or staff convenience is not the best way to go ... tho sometimes it has to be. If spam is too much of a hassle, that area may just need a bit more resources invested in it.

It could for sure help, to have different spam-control methods on Posts of different ages. Keep current-topics wide-open, then after a week or 2 or a month, make the commenter jump through a little bit more of a proof-hoop, and finally after a few months or so, shift the burden of proof that one is a human more-fully to the visitor. We have the templates & CSS to support that. A plugin could probably be forthcoming.

That way, you got the free-flowing action for current stuff, and more-effective spam-security for the old stuff ... without slamming the door & shoving the bolt home.
====

I believe there is an SEO benefit to having on-going commenting ... and that optimally, the clever Admin will even find ways to actively encourage continuing input on posts. You realize, eh ... this is substantially the explanation for the fact that I am reading *old posts* ... and seeing comments still being made on them. The Engine is showing me the 'active' stuff, ahead of the shut-down archives. Hmm? :)