It's always useful to have a dozen terraformers and miners and cargo units laying around pre-built, as these are very nice items that never refit with tech. Upgrading your magazines makes your old ammo obsolete, but terraformers never go out of style.
Speaking of auto-tugging, I'd love to see the command possible, to order an engineless ship "request tow to X" and then have one of your idle, specially designated TF go fetch it. You could make tugs that are assigned to a planet and/or sector, and automatically perform any hauling within their area. Would make things SO much easier. Kind of like civilian shipping lines, only it's a tug.