Pretty much this entire discussion will contain spoilers, so mouse-over at your own risk, and if you reply, please use spoiler tags.
I recently captured a bunch of Precursor ships. I ran into a system with multiple fleets protecting two different installations, and they eventually merged into a large fleet that I was not able to beat until I could collect my entire empire's fleet together, plus build a few more PD escorts to handle the debilitating AMM spam. I was finally able to defeat their fleet, leaving a string of their disabled ships half way across the system, with fairly minimal losses on my side. I then boarded and captured each ship. As a result, I now have about 600ktons of Precursor ships, which nearly doubles my empire's military tonnage. However, their tech is about one level below mine in most areas including ECM/weapons/sensors etc.
The first big issue is that the engines have NO fuel efficiency tech at all; they're still using one liter per engine power hour. Even getting them home to a shipyard where I can repair them will take 45 to 60 million liters of fuel, and that's a significant disincentive to try using them offensively
The other big issue is that about half of that tonnage is offensive missile ship, and up to now I have avoided using missiles at all. I did recently started building some small fast ASMs to distract enemy AMMs and keep the AMM spam off my fleet, but I haven't built any ships to launch them yet, and I certainly don't need ten 30kton missile cruisers to do so.
Hence my question is... what should I do with them? I could park them in orbit around my home planets, load them with legit ASMs and never use them unless I get attacked. I could try to re-engine the non-missile ships with more fuel efficient engines and use those either offensively or as colony garrison forces, but there's quite a mix of ship classes and I'd have to retool for each class to do so. Or should I just tow them home using civilian tugs and scrap them for minerals? Most are pretty heavily damaged, although I repaired the essential components (engines, fuel tanks, and crew quarters) using MSP from my fleet support vessels, so I may not get a lot of useful components out of scrapping them.
I guess one other option would be to SM in some more reasonable engines (still at the lower engine tech level, just with commensurate fuel economy tech, with the rationale being that it's a game reason (NPCs don't use fuel until 1.14 I believe) that they ignored fuel efficiency, and real ships at this level of tech would be better.