This is as obviously someone's highly valued rifle. Only somebody who used that Spencer to hunt a lot would have gone to the expense of customizing it. The wear marks indicate, one assumes, putting meat on the table. It is a real beating swords into plowshares story. That gives this Spencer a very interesting story.
You can return it to a military appearance at some expense. Then you would have a wall hanger with replacement parts, i.e., of low value monetary or otherwise.