Currently 3 autoflags is the amount used. It takes 4 flags to delete a post, so there is currently 1 human in the loop, but not more. There is basically no point in casting more autoflags than this, as long as you are unwilling to remove that 1 human in the loop.
However, I do think that we should go to 4 autoflags and autonuke posts that are certainly spam.
It is easily possible to make SmokeDetector conditions which catch a lot of spam and are perfectly accurate. For example, in all of the time SmokeDetector has existed (since 2016), there has not been a single false positive with more than 5 "reason weight" and more than 4 detection reasons. But such posts encompass 49.78% of all spam that has been posted to this site.
We can do a bit by adding another condition, and autonuking any post with more than 273 "reason weight" (again, this condition has perfect accuracy). Between these two conditions, we've now encompassed 50.62% of the spam on this site.
But, we can also encompass more spam in our perfect-accuracy autonuking by using keywords. For example, 34.03% of all spam posted to this site has contained "helpline" in the title, while no non-spam post ever has. Of these posts, about a quarter (there isn't an easy query for this, and I don't want to go through all 4k+ posts manually, so this is based off extrapolating from a random sample of a few hundred of the matching posts) wouldn't be caught by our 2 conditions from before, so about 8.51% of all spam. Adding that to the conditions above, we get 59.13% of spam that could be easily autonuked.
Given that we can clearly get rid of the majority of the spam posted to this site automatically, without the spam staying on the site until someone flags it, and without people needing to interact with the spam, why wouldn't we do this?
Frankly, I'd imagine we could probably have better conditions than these, that would catch even more spam with perfect accuracy (after all, I came up with these in 5 minutes).