Having been involved for a number of years, in the restoration of antique furniture and other "old stuff", I have a couple of thoughts to add that may be usefull.
The current rage against restore/refinish/renew, etc is in the main, the result of a misunderstanding of the value of "oldness". The exclusivity of having some thing that appears as it did "back in the day" has a definite impact on value. However, the ability of a thing to serve as a historical document has traditionally been the truer arbiter of an antique's value. I don't think many "Antiques Road Show" fans or most of the general public are aware of this. Instead, the "urban myth" that everything is better left "unrestored".
One way to look at "old stuff" is to consider the relative rarity of the object and the likelihood that it will remain a viable object into the future.
When an object is "rare and original", it has a high value because it is a historical document showing among other things, how the object was made and the nature of its constituent materials. However, one might want to weigh the value of originality against the usage value of the object; that is to say, if you want to have
this thing in the future or if you want to use
this thing, you may want to repair restore refinish yada, despite possibly
lessening it's value as a historical document. In the end, the thing that survives into the future, though restored may be more valuable than the thing that becomes original but useless trash.
And of course, any and all of that may have nothing to do with market value...