The KP2 is a keeper in my eyes. I wanna tell you to hold onto it because they are special pieces. I have a KP that's still in the process, stock needs work and some rust removal. But it's yours, and your choice in the end
I'm afraid of pricing your Kp because I might try and buy it. With the current work and condition I wanna say it's gonna depend on how much you wanna squeeze out of it, but that's just me as I hold these in high regard. Most of the time modifications should devalue the marker, But what you had done is acceptable work to keep the performance of the marker in top shape.
So I'm just gonna talk out the side here and say keep it and get the stuff you want done on it. Make it your perfect rifle. PPS kp's are valuable as well and certain mods could in fact raise it's worth and longevity.
Oh yeah, welcome to the MCB family
Edit: I'm just gonna let someone else price that...