Yes...Colt did make the Trooper in electroless nickel. Colt called it Coltguard. I've seen them in a satin finish and a more highly polished finish. I've also seen a matte finish electroless nickel but mostly on the Lawman Mark III which was the low buck .357 version.
Are sure of the trigger pull at 4lbs? Is that the single-action pull (I hope so). The factory sent them out with about a 15-16lb double-action pull. I doubt if a gunsmith did any work on yours as there's little that can be done due to how the gun is made and parts hardened. The only real way to lighten the trigger pull is to replace the mainspring which may have been done to yours.
The Mark III is an excellent heavy duty revolver...short of actual abuse I doubt if you can ever wear it out. It will serve well for several generations of owners.
As far as value...the electroless nickel examples bring some premium against a blued example in equal condition. For .22LR, the 6" barrel version is probably the most common...4" less so which may bring a slight premium. I know the .357 Mark III was made in an 8" barrel version but don't know whether any were .22LR. There's also a .22 Magnum version as well which likely brings a bit more money.
My Coltguard Trooper Mark III revolvers in .22...