[Suicide Junkie]

Your repair crew is the absolute minimum number of people required to keep everything running. If you take on a big job like a retrofit, you hire more people or pull them off other projects. And your industry has to build the spare parts, which could have been used on a brand new ship, etc. etc. (I don't think you'd keep a spare ion engine just lying around, if you need something big like that you build it).

No, your repair crew is the space and mainteance you pay on that space station's repair bay, (or the repair ability of the space yard).

Using the repair ability dosen't cost your economy anything more...
Not using it causes your resources to go to waste maintaining an idle repair bay.