It will not hurt the value.. its a rather simple upgrade.. however cutting an IEC is not an easy task without the correct tools.. the shape, the fact you have components inside you want to stay away from physically etc... Forget the Nibler tool at a radio shack or anything like that, you would need a good template with a dremel cutting tool most likely to do it more professionally.
Other thing to consider is depending on where your Hot, Neutral, and ground wires are connecting inside from your new IEC it would be even more effective since your worried about wire quality using a new cable in the first place to actually put a good power line type 10 gauge or 12 gauge wire internally to the power supply as well feeding from the back of the unit. Then you eliminate the cheap 16 or 14 gauge wire all together.
This again will depend on your skills, but its easy, and really will not do anything to effect this kinda amp in the "Vintage" market as they are pretty cheap anyway and anybody would welcome the nice update in this case....As long as its done in a clean and professional finish.
Whether its gonna be super effective sound wise or not, or worth this effort and cost in the first place will be for you to decide, unfortunately no way to know until you basically just do it.
The cost of materials with slight soldering and machining skills will probably be cheaper than shipping it back and forth with insurance due to the size and weight of the unit just as a warning!
By the way I think you mean Female IEC chassis socket. I believe the male is the standard on the Cable end you refer too.
Good Luck
