[Puke]

this would be a pretty heavy game change (and its not a totally original idea), but how about this:

planets generate a minimal ammount of resources. to get more resources for your empire, you have to recycle ships. recycling will give you more resources than the original construction cost.

Freighters could be of three types - an all organic hull, an all mineral hull, or an all radioactive hull. It would have to have built in movement, and such. colony worlds could have "freighter construction" spaceyards that are good for constructing nothing but freighters.

The reason you recycle them at your homeworld instead of where they were built, is that your homeworld starts with a recycling faciltiy that gives a significant bonus to recycling income. It may not be proffitable to recycle the ships without this bonus.

The reason that you would want to build a limited freighter spaceyard instead of a general purpose spaceyard, is that freighters would take a year to build at a regular yard - but a freighter yard would have 10x the build rate. due to the high cost, freighters would have to have no maintenance.

also, the high cost (and relative short build time) of a freighter is a reason that you build and recycle them, instead of just building and recycling regualar ships (which would also be good for combat, or whatever).

cheers