That is a beautiful rifle! Does the stock increase or decrease the value? Well, that depends on who you talk to. To a purist collector, any deviation from factory original condition decreases the value. On the other hand, to a "wood freak" such as myself, who also loves the 358 cartridge and the Savage 99 rifle, and appreciates that for the beautiful and functional hunting rifle that it is, as do I, the enhancement increases the value. The only change I would make if it were mine would be to replace that ventilated recoil pad with a solid English style pad, just my personal preference.
I would think that that rifle would be worth from $800 to well over $1000, just depending upon getting hooked up with the right customer.
Best regards, BIGBOOMER