However, I am getting tired of having to do things that in the end do not matter. First among these is units appearing in random cities. Yes, it is realistic, but it makes no difference to game play. You just go around spending 5-10 minutes each turn dragging your newly built units to a couple of marshalling centers in each theatre. I would argue that this is a waste of time: it does not add to game play and it is not fun.
By contrast, organizing your units into divisions (and re-organizing...) IS fun because it DOES affect game play. You can create an artillery-heavy siege and defense division. You can assemble all the militia in a division with a militiaman leader. You can optimize how divisions are put together in a zillion ways that actually affect game mechanics. I do not mind micromanagement of that sort (I've spent more hours than I dare think about eking the last fractional economic point out of the construction rules in Federation & Empire

So, imagine that it made a difference where units come from. Suppose each brigade had not just a state of origin but a city of origin. When that brigade took casualties, the loyalty in that city drops, when they are part of a glorious victory it increases. Now where a unit comes from has a game mechanical effect, and I would not mind finding and moving all those reinforcements. I'm not claiming this is a good idea, BTW, I'm saying, given that the city of origin of a reinforcement does not matter, please, let there be a mod or option to just have them show up all in one city per state. Logic-wise, it is very simple: instead of having reinforcements show up randomly in a list of cities, just rank-order the list and put them all in the first city on the list not enemy-controlled.
At the moment, it does not appear that there is any game effect (except for Militia) of which state a unit is from originally. I used to think "oh, better not recruit all from one state, the populace will be unhappy because the burden falls disproportionately on them". Other than counter mix limits, however, this does not seem to matter. So really, you could even do away with the per-state reinforcement system. I would prefer state affiliations to matter though - maybe what happens to a brigade should affect the loyalty of its home state.
In conclusion, my goal is to maximize fun over time. Micromanagement with no gameplay effect is the enemy of that.