Bitcoin isn't the most advanced cryptocurrency out there. It doesn't have even close to the best technology. Bitcoin's continued dominance is very strong evidence that it's completely popularity, not technology, that drives prices. There are numerous other examples: Peercoin, for example, pioneered a new proof algorithm, but peaked at $10 and is now at $0.38; superior technology doesn't guarantee success. This means that it's entirely possible for another cryptocurrency to surpass Bitcoin, but the technology isn't the driving factor.
With gold, there are industrial uses which drive the price up or down, and you can't just substitute platinum or silver for those industrial uses. You can substitute platinum or silver for gold as an investment, but the laws of physics limit the number of precious metals that can stably exist, so gold is competing with a limited number of precious metals as an investment. Not so for Bitcoin: I can spin up a competing blockchain this afternoon if I want, and there's no limit to the number of competing cryptocurrencies.
What I'm saying is that I think that speaking of Bitcoin as "digital gold" breaks down pretty fast once you analyze it at all.