> they have to store some of it somewhere. This is one of the uses of currencies

Currency is for current things. You don’t store wealth in currency. Even in poor countries wealthy people store wealth in assets, be it real estate, businesses, cars, or cattle. Only poor people store their “wealth” in currencies, because they can’t afford any assets.

> there is no incentive for people to keep pouring money into it, so its value relative to Gold, USD should not increase too much

If there is no incentive to keep pouring money into it — not feeding the miners who maintain security and turning gears of the network — then indeed the value will not increase, but rather rapidly decrease.