IMO, case and accessories should match the gun in question. That is, a high grade gun in high condition is expected to have a high grade case and accessories in high condition. If it doesn't, it will get dinged up to several thousand dollars. A low grade gun in low condition is not expected to be cased or have accessories. If it does, it will get up to a few hundred dollars (about the independent value of the case and/or accessories) premium. "Expected" means that the market has already factored in case and accessory value and changes will draw a premium or a ding as reality varies from expected.
Provenance is a hard sell except in rare instances. You have to have a very rare, historical situation to get a large premium. Many Americans find it interesting to learn the history of their guns. However, only a few will pay really big bucks for "museum" pieces. Toby Barclay does a wonderful job of documenting the guns he sells and he does get some premium for so doing. On the other hand, it is not unusual to see guns well documented to minor historical figures fail to make "hopeful" auction reserves.
