I've got an idea on how to make autogrouping more usable and less annoying. I suggest to rework it so It will work this way:
Defaultly It won't group any nearby objects or anything while placing. But as soon as you hold [Ctrl] it will place the object in group with the nearest object (You will be able to modify the activation distance). If you keep holding [Ctrl] you can place multiple objects and all of them will get grouped together as long as you hold [Ctrl] - you stop holding this key - it will stop placing multiple objects as usually. It will be very simple, comfortable, usable and practical.