On the one hand, I buy the concern for "more trouble than its worth" -- not because it takes new code, but because it would require all of us (yep, /me included) to amend the (quite reasonable) attitude/behavior that 'all posts should be approved, and promptly, unless they're trolls, obscene... etc.' And changing that attitude/behavior would probably take time.

But, OTH, if (and it's a big "IF"!) the notion in the OP has major merit (and the --votes indicate that some disagree, though one could wish they'd spell out their critiques), perhaps that would be worth it.

As to your thoughts on a "test," that seems to /me to have great merit... but merit which I fear would be offset by the extent to which it would discourage newcomers. We see many of them post on their first visit... because they can. So while "mess" is an indeed genteel characterization of some of those first-posts, many others reflect great care in their preparation.

Admittedly, that may be tantamount to saying their authors practiced at least the "little learning" you speak of, which, in turn, suggests to me (anyway) that they'd promptly pass the test which argues against the concern we share.

But, my bottom line still comes out against testing, not because of any problem with viewing testing as elitism, but because it might obstruct participation by new folks and drive them, instead, to some of the truly dreadful advice rendered elsewhere.