I've never upgraded a project gun significantly. Reblue, restock (only once, to fit me, and maybe a nicer piece of wood, but, nothing out of line) recut checkering, new pad, etc. More along the lines of maintenance to mechanics and finsh. Might just be me, but, I like the way a low grade gun looks when it's all cleaned up. And, I suppose, I'm cheap.
Best,
Ted