Send it to Colt and have it done right.
Get a local bubba gunsmith to do it and you may save a few bucks, but if they don't know what they are doing particularly in the prep, your gun can be quickly destroyed or degraded as far as any future value. Aggressive buffing can round edges and cause stampings to disappear.
You get what you pay for. If it is an heirloom Colt. You can't beat the Colt Custom Shop.
I would disagree that a re-finish always decreases value. Your average shooter grade gun needing a re-blue is not a high end investment to start with. One caution, you could wind up with more in the gun than it is worth depending on initial investment. Example: You pay market vale for the gun - and then drop another $250 in a re-blue, your upside down in the gun. Your not going to hurt your retirement portfolio having your Dad's Colt Trooper refinished at Colt.
I've seen some older higher end guns that were refinished/restored by some of the bigger names in this craft, such as Turnbull, and David Chicoine that have actually increased their value. Again you have to weigh the cost of the work being done against what you have and want.