My interpretation of the premium value add to a gun with the Bright Blue finish is in the context of what was the standard finish of that model at the time of production ?
In other words, if it was a post WWII gun that was normally finished in the more satin service blue and it was special ordered (at extra cost to the consumer) with a Bright Blue finish, it commands a premium due to the scarcity compared to other similar guns made at the same time that had the standard finish.
The SCSW says Bright Blue became the "standard" finish again in 1956 so if all guns made around the same time were Bright Blue I don't know that it would command much of a premium except that would be more aesthetically pleasing.