Guys think of it this way..
If you were really in charge of a whole base so to speak, would you be able to command all of them at once... some times maybe but most likely no... think realistically 12 at a time is good, if you want to plan a mass attack do it like a real commander would.... Use your Ctrl 1..2...3..etc. If any thing I think 24 can still remain realistic, so I vote to change it to 24, but no higher than that... One thing is for sure there should be no cap of guys you can make, the 200 in SC1 is horrible, say your in a 20 min game playing fastest map, against a zerg with like 30 hatcheries and your protoss... even if your a good protoss, you wont be able to win against a decent zerg... simply b/c it takes zerg 1 minute to build 90 hydras and takes you, 1 minute to build 30 dragoons if your lucky. Yes I know there are templars and all that... but if you got 50 probes which you more than likely will you can only make 150 guys tops, and most Protoss units take up 2 PSI, so the mass for a zerg will crush you eventually... your only bet is to keep making arbitors and recalling his money every chance you get. Zerg will just stay maxed the whole time while on the other hand you can't.

So I think the units you are able to make should be unlimited... If there is a problem with the servers not being able to handle that... fix it, you got games that are able to have 60+ players playing on the same map at the same time... yet you cant handle 8 players with 400+ units each. thats just nonsense...