Technically, Treasure doesn't need to be anything big or fancy. It can also be thought of as 'salvage' since its stuff left behind that can be picked up and either recycled or reused. I'm against 'super powered stuff' because that's just guys looking for an easy out. Make it stuff we can save/sell or recycle into usable things. Like ancient weapons that aren't usable now but can be recycled into usable resources, maybe some very rare. The other things that can be used but only normal everyday things the Arkadians used for their everyday life, maybe decorative things for apartments, but also weapons/vehicles/armor/specialized scanners for things like enemy scanning. Theres an endless assortment of things that could be called 'treasure' to a new civilization just finding it, and much would be things we have no idea about, since it is something we never saw before, it can be marked 'unknown technology' and sold to archeologists or scientists in the citys for a flat rate, and then days or weeks later new technology appears from their research things like that.