Who actually trims Pistol brass? I guess I am a bit put off by the thought of it, as I have thousands of 9mm cases that I load with some regularity.

As long a sthey are within specs , you are ok. However, if you are roll crimping, all need to be the same length. If taper crimping, you can get away with a little more variation.
I load on a DillonSquare Deal B, and it's been a long time since I have trimed, but I use all Cowboy Action loads

My revolver brass doesn't stretch so I don't worry about that. I do check my 45 ACP brass though. Autos seem less forgiving especially if the brass gets out of spec. By a LEE trimmer it is much faster than setting up a trimmer. Then work on a 100 or so cases a night. You'll have whittled through them in no time and not had the agony of trying to go through all the cases at once. Sean

I don't trim revolver brass, but do keep them "flying in close formation". If one dies or is lost from a batch, I don't add a new case but keep them together until they die from splitting or other fatique. .45 ACP brass are my primary recycled pistol cases, I do watch these. If too long, I dump them. Brass is cheap compared to labor to salvage them. I might add I buy the cheap reloadable rounds in most cases, after the cost of bullet, powder and primer are subtracted, the cost of "once fired" brass is minimal.