My tire's valve stem is stripped (both top and middle section) that I cannot even put a cap on. Is there a way to fix the thread without replacing the whole thing?
To me it looks more like it's not round anymore (taken a beating). In your case I don't think there's much of an option besides getting a new one installed. You could try to put a die on it of the right size and get the threads worked out ... you'd be in no worse shape.
As an aside, while not optimal, if you're not leaking air, you don't really need to worry about it too much. If it isn't, I'd suggest getting it replaced at the next tire change.