So in my ongoing quest to fix the high idle on my 1999 Altima, I decided to
back out the throttle stop screw a little bit and see what happened.
It says right in the service manual, "Never Adjust!" but I decided this was
one of those times where you have to ignore the warnings and give it a go.
It looked like it may have been messed with before, anyway.

About 1/2 turn was all that it took to get my idle down to exactly where
it's supposed to be, around 750 rpm.  Any further turning didn't do
anything, because the throttle was then resting on the fast idle cam.  I
went for a test drive, and everything seemed to work fine, the car felt
noticeably smoother when getting onto the gas lightly and when letting off
and coasting.  It also behaves like my '94 when putting in the clutch now,
coming to a stop, whereas before it would rev up to 2500 rpm when I'd come
to stops.

The only problem I ran into was the throttle was sticking occasionally, but
a quick wipe of the throttle plate and body with a rag and some cleaner
seems to have fixed that.

I checked the throttle position sensor and closed throttle sensor, and they
both seem to be within spec.

So, is there any reason I couldn't or shouldn't leave things as is?  When I
unscrewed the stop screw, it and the lock nut came out together, so they're
still fused to each other, which means I could put things back as they were
just by screwing it back in.  I also marked everything with a marker before
I started.  But the way things are now, I can't see why I couldn't just
thread the screw in until it's against but not actuating the throttle at
all, snug down the locknut, and call it a problem solved.