Here is some book value averages for comparable versions. In either case if you bought at MSRP and kept in 100% finish (unshot) you would have gained a little value. If you used it regularly, but kept it in good finish (95%), you would have lost a little value.
GP100 in Stainless
In 2006 MSRP was $580
In 2018 100% is $625 and 95% is $495
S&W MODEL 686 DISTINGUISHED COMBAT MAGNUM
In 2006 MSRP was $667
In 2018 100% is $725 and 95% is $600
The Colt Python is an entirely different matter. Colt collectors are the most fanatical. And you have heavy movie/TV tie ins so entertainment collectors are in play as well. And then you have shooter demand for a model with no current comprable being made.
In 2006 a common Colt Python in 100% was $950.
In 2018 a ccommon Colt python in 100% is unlisted (sky's the limiit in auction), in 98% is $3,500, in 95% is $2650
Few other revolver brands will hold value as S&W, Ruger, and Colt. These are the classic revolver brands with lots of attention and history.