Now that is an interesting question. Lets pretend the guitar is just the guitar, and Neil Young has nothing to do with it. So C.F. Martin and Company switched to Indian rosewood in 1969, okay? Everything I've read says Neil got the guitar, as a gift from Stephen Stills, in 1969. That does not mean the guitar was a 1969 model. It could be, or maybe Stills bought the thing in 1968, there's no way for me to know, but the difference is really significant.
I'm going with 6-8 thousand dollars based on the make, model, and year of production, and then the difference is based on what kind of shape the thing is in.
Myself, I think Indian rosewood is undervalued in some regards. I feel this way because I own a Brazilian rosewood guitar, and it is invaluable to me, but Brazilian rosewood likes to get cracks in the sides. The cracks tend to not pose significant problems, but they are unsightly. Nevertheless, Brazilian rosewood is something people lust after these days, and supply vs demand economics teaches us all that such things increase the value significantly.
Now once you add in the important fact that Neil Young owns that guitar? Buddy, you're talking about someone who's worth millions and millions, loved around the world, and so, that guitar is worth more than a million dollars, I suspect.