[Nitram Draw]

I like Tenyru's idea about ramping up production. This is the way it is in real life, you just don't immediately switch production of a new item to maximum.
Another idea on this line would be to have an increase in cost when you switch between items. If you build 5 of the same ship in a row at the same yard the cost per ship and time per ship could decrease as each was built. This would allow you to have yards that build specific ships faster than others.