I don't think it has been reblued or dipped. Occasionally you will see locking block pins, blocks and springs blued from Spreewerk. Nothing unusual there. You have to look for other telltale signs of dip...like the sear. Should never be blued (tends to turn more of a brown on the Russian dips).
The grips (from what I can make out) are a mixture of Walther and Posselt grips. The left side is definitely a Posselt grip panel, and right looks to be Walther or maybe AEG.
If you paid $800 for it, I'd say you made off well. Really depends (a LOT) what the other guns look like. To get up into the $1500 range, there are a number of factors involving Spreewerks. Typically, you have to get into the early (no-letter block) or later guns (zero series a/b-prefix) to start drawing that kind of money. Flat mint guns may draw that kind of money if they're early or late (excluding the one-off auctions). But Spreewerk guns can be kind of a mixed bag of auction prices. There are a lot of little weird oddities to Spreewerks that can attract collector interest, like the backwards 'c' block pistols, or the FN frame pistols in the 'x' block, or the upside down or sideways 'cyq' stamping...
BTW, what magazine came with it and what kind of condition is it in?
Really have to see some good pics of these other three to tell you anything else.