I have another thing that I have been thinking of lately in regard to balance... I think that shipyards that are doing any sort of construction such as expanding the size or adding slipways should get half production capacity if it also are building any ships, or reduced production capacity based on the number of slipways currently under use.
The general issue I have with shipyards is in comparison to ground construction factories, here you have to actually choose if you want to build more factories or something else.
I'm not saying this is a huge issue as you are still dependent on mined resources, but the shipyards are in general terms really effective once you start pumping out terraforming, orbital mining bases in their own dedicated yards. As you can keep building these while expanding the yards to build even more of them.
In order to curtail the snowball effect a bit I would suggest that yards get an efficiency modifier based on how many slipways are in use at the same time, up to 50% if all of them are in use at the same time as it does any sort of upgrade on itself. If you don't want it to be as severe you could make the max penalty like 33% or 25% instead, or you could turn it into a new tech line that start the penalty at even worse like 75% (you loose overall productivity if you multi-task) and then reduce the penalty down to a much smaller one at really high technology.