Although the Historian alters wrecks that doesn't mean you should ignore wrecks, when approaching one you might get an event that your crew finds a hidden compartment holding something of value, in one case I found an Astral blueprint on a Kite.
It is possible, but the odds are low enough that I do not bother. I usually treat pre-placed wrecks as storage of sorts. If I do not need it, leave it until I do need it (which is usually never).
Another wreck to leave wrecks - missions. Occasionally, they post missions on a wreck I found but left alone. Easy money and rep.
Does anyone know if you can get any other colony item's in ruins besides synchrotron cores? Are drops planet type specific?
It is random. In the game I played, I got mostly Soil Nanites, Cryoarithmetic Engines, and Combat Drone Replicators. In other words, insignificant crap. Also stumbled on Plasma Dynano, Orbital Fusion Lamp, and Hypershunt Tap, none of which I needed. As for nanoforges, I stole them from the core worlds. Historian would have been the only other option to acquire it from. I also found one Synchrotron, but reloaded the game and forgot where I found it, so I ending up stealing it from the core worlds too.