Does a reblue have an adverse affect on gun value?

To a collector.

If a re-blue, or any refinish that's done on a whim so as to change the appearance of an otherwise perfectly fine original finish, then yes, to a collector, the value may be diminished. On those hand guns, or rifles for that matter, that have a finish that is so worn or damaged that the cosmetic appearance is not only extremely unattractive in appearance, but that the mechanicals may be suspect due to the poor condition of the weapon, then a restoration of said piece, followed by a re-blue would be in order. I had a Sistema 1911 that I brought back with me several years ago from South America...the gun, while functioning, was a total basket case cosmetic wise. I paid $50.00 American for it, spent an aditional $450.00 in restoration, that included replacement of most internal parts with Colt factory parts, rollmarks re-stamped/engraved, sights replaced, and a Carbonia blue re-finish. I sold that gun last year for $1600.00 because of the restoration and re-finish.

I collect 1911's, and those I find on sale that have been cosmetically altered with a "paint" job, or lowering and flaring of ejection port, or have added non-factory standard accessories such as sights, checkering of the grip, etc., I reject...those examples have less value to me then a gun that is still in its original factory configuration.

While there are occasional exceptions like the one previously mentioned, in most cases you never recoup the money spent on a refinish.

I had my 586 done, and I think it was worth every penny. It was ugly, now it's not. I'd never get the money back if I were to try to sell it, by luckily, it ain't for sale.
As was mentioned, from a collector's point of view a re-blue can be a bad thing. My 586 will never belong to a collector.
From a shooter's point of view, it just makes an ugly gun pretty again.