If you want to get the most ammo flexibility out of your SKS, you need two separate fire system sets. Keep the original bolt and trigger group unmodified for surplus or berdan primed ammo. Then acquire another bolt/carrier and trigger group modified with a Murry's firing pin and lighter hammer spring for the boxer primed ammo. Getting the proper head space will be an issue so you will have to buy a few stripped bolts to be sure. A tuned recoil spring wouldn't hurt either.
Yeah, it looks to be allot of work, but this way you can get the most out of your SKS. I would a agree that most accuracy/reliability issues with the SKS are attributed to improper care and maintenance. It is a great gun, I see no problem spending money on a "cheap" gun.