I say heck yes to unlimited troops, as long as you have an economy to support them. I mean if you had a surplus of materials, you could overbuild and still have enough resources to maintain your army for a few months while you wage a particularly heavy campaign in one corner of the galaxy.
Yes I'm talking about maintenance costs.
I think maintenance cost is a far better alternative to having a max army limit. Admittedly there may be a limit on how many one Army can be, but not on how many armies you can have and how full they each are. (yep, this game sounds really close to Total War in my head)