At the moment Police Positive Colt's are not a hot item with collectors, but interest is growing. Don't reblue it by the way, because what's on it can't be duplicated.
Shooters seldom buy them because they are chambered for the .38 Colt New Police cartridge (same as .38 S&W) which is sometimes hard to find, and generally expensive.
That said, they are fine, hand-built revolvers that offer workmanship you don't see today, and is one of the Old Fuff's favorites. I generally see them selling in the $250 to $350 range when they are in almost-like-new condition.
Personally I would keep it. I don't think the value will go down.
One last point: The Police Positive and Police Positive Special revolvers were numbered in several serial number series, and because of this they are sometimes mis-identified as to date of manufacture. I suggest you post the serial number (use xx for the last two numbers) to confirm when it was made. You will find the number stamped on the frame, under the back end of the barrel, behind the crane cut-out. You need to swing out the cylinder to see it.