A bit of info:
Installing Colt Target grips on a Python may or may not increase the value.
An average shooter wanting a Python might pay more if it has genuine Colt walnut Target grips.
A collector would likely pay less unless the grips are the correct type for that specific Python. Usually the original grips for a stainless Python were rubber, usually the Pachmayr Presentation with Gold Colt medallions.
Whether a seller will attempt to price a Python higher because it has genuine Colt Target grips depends on the seller, and whether you're willing to pay more for grips that are not "correct" for that gun.
You can still buy original Colt target grips of three different types, but the price usually starts around $300 and goes up fast.
For non-Colt grips you have many choices ranging from less then $100 an up.
Good choices are the Hogue Mono-Grip that is made of fancy hardwoods and have options like without finger grooves, and the Altamont laminated wood grips. These come in several styles, including some that are reasonably close copies of the Colt Target type, some with laser carved Colt logos and designs.
I'm sure someone will correct me if I'm wrong, but I believe the type of grips for a SS Python has to do with the date of manufacture. The early satin stainless came with the walnut grips, while the later productions came with the rubber. The bright stainless were manufactured at a later date and therefore came with the rubber grips. Sometimes you could specify wood as an option, which could be noted in Colt letter.