A 1951 Winchester 94 that needs a bluing job is worth $400-$500 on today's market. I have bought a few for less. So I am pretty sure my price is at the top end of what they are selling for(not what some idiots are asking).
I do not thnik a professional rebluing job would reduce the value that much. Actually IMO the Pre-64 94's are sought after by hunters who wish to use them. Now by that I mean rifles built in the 40's, 50's, and 60's. Earlier rifles are real collector models and should be treated as such.
If you want to use the firearm for its intentions(hunting). They go ahead and have it reblued. It may reduce the value a bit, but if you are keeping the rifle to hunt with then who cares.
However I would do as mentioned above. I would have it professionally done by a competant gunsmith. Cold bluing just does not work right, or look good.
I hunt with a 1958 Winchester 94 that also could use some bluing. however I choose to carry it in the condition it is in. I consider the wear to be beauty marks.
Below is a picture of a 1958 model 94. Notice the small pitting at the bottom of the receiver. This is due to carrying a rifle for many years. If this is the problem you have with yours then a rebluing job would not help. The pits would still show. Tom.