Yes, thank you. But:
your exame is different, because after that the gold value falls 20%, you have to buy gold, and you spend your money from your wallet.
When the value of the GHS falls, you have buy more GHS, BUT you will spend the BTC which is produced by your GHS, so the amount of your investment not changed.
Isn't it?
Well, yes but now you are really discussing the coin which I agree is different and I only used gold because that was the example proposed earlier. Plus of course it is a little bit easier to work an example!
In the case of the coin and the GH/s vs BTC; I agree the GH/s you have will generate BTC; and you can use that BTC to buy more GH/s.
However:
1. you are still spending actual BTC
2. the reason for the fall in the GH/s price is most likely because the difficulty is increasing and, therefore, the GH/s you buy will generate less BTC
Really it is going to be very interesting to see if the rate at which GH/s can be acquired (and the resultant return of BTC) will be sufficient to maintain a strong value for the coin. I don't know the answer and I'm not really sure how to go about working it out, though I may give it some thought - it is an interesting problem!
Moreover, it is only one element in determining the success of the coin and as pointed out one that most other coins don't have.