As with so many things among collectors, worth is often in the eye of the beholder. No question, a rusty Colt Single Action Army from around 1873 could be worth thousands of dollars, and its value diminished by trying to restore it. However, a .22 rifle branded for Sears, rusty and non-firing, not so much.
DIY: How to Resurrect Old Guns
DIY: How to Resurrect Old Guns