Consider that if you are asking these questions, the next buyer will also. So, you will have to take the appropriate discount when you purchase and understand that you will have to give a similar discount when you sell. "In-proof" is helpful, but I don't think SJW did it- are you refering to SJW steel barrels?
To answer directly: The rechambering will drop both the desirability and value of the gun. I shoot several guns that were rechambered, using appropriate loads, and it doesn't bother me a bit. "Warts" is pretty much a fact of life for those who collect and shoot older guns; your comfort level and wallet level will dictate how many and how big "warts" can be on your guns. Originality increases likely ease of reselling and value retention. However, price will always be the key; any gun will sell at the right price. Getting top market price is what takes awhile, high condition or not. Purdey is always desirable. "White elephant" is a function of price.
