Most hubbers would say the answer to your question is yes. It's best to aim for at least 800-1500 words for an average hub. Your hub on travelling Australia by train is a good example of what to write.
There are occasions where shorter hubs are fine to do but still make them 600-800 words in length. Remember you need at least 300-350words to get the main adsense advert at the top right of your article which is what you want to be aiming for. It really depends on your topic but 500 is on the short side- just my opinion.