Yes bitcoin is more scarce than gold. That's a true statement! But if you look at the acceptability of Gold and bitcoin, gold is a clear winner. Scarcity alone doesn't make something costlier. It has be adopted and accepted widely. That's how you can bet on its future value.
Bitcoin is a very new asset class compared to gold. It has a long way to go! So instead of drawing a comparison between these two assets, let's help in bitcoin adoption.
As of now the acceptability of BTC is not too wide. If its the basis for the comparison, gold is prbably preferred.
Thew world.however is preparing to go digital which if currencies will be back to gold standard like what China and Russia plans to be. I think digital currencies backed by gold and BTC will be accepted as medium of exchange.