DFNewb,
Thanks - but if I need a large enough Yard to upgrade the components is it still worthwhile using Construction Factories to build the Installation first rather than using a Yard to both build and refit.
DavidR
You will still build it much faster with factories.
There are two benefits of building these with a yard:
1) You get to use your factories to build other things during that time.
2) You make a lot of wealth from the yard workers. A 250kT commercial yard employs 6.25M pop per slip. That's a lot of worker taxes.
All that said, it's a massive investment to build such a yard, and it would take a long time for the income to pay you back.
Personally, throw a lot of extras on my enormous stations.
Usually sensors (all three types) and a fuel tank and a refueling system, at the least.
My rule of thumb is that if it adds less than 1% to the cost and weight, and it might ever be useful at some point, I throw it on there.
But I don't think I would ever bother to refit them. They are just nice-to-have little extras on the design. Not worth the hassle of trying to upgrade them later.