I have been chasing that PSG dream for a while now and came across this auction ( https://www.gunbroker.com/item/868560562 ). Its a beautiful rifle but I have to ask 1. Why replace the scope other than damage and 2. How badly does that affect the value?
The other reason to replace the scope besides damage is to upgrade to a more modern and advanced optic which if you decide to shoot the rifle will make a big difference. The original scope is pretty dated so if you can get a set of rings that work with the PSG1's welded-on mounts, then that just opens your options up to a ton of more advanced optics.
In terms of value, if you're a high end collector looking for originality, it really decreases value. Even with all things being equal, one PSG1 with the original shipping cardboard box could fetch hundreds if not a thousand+ more for the collector that want it all. That's why they call us collectors crazy. Which I can't argue, it's a sickness. ;)