It depends on what your goal is. If you just want to get published quickly, then short and sweet are ok. If your goal is to get readers, and passive income (Adsense, Amazon, etc) then you need to grow your hubs. To attract readers and place well in search engine rankings you need to have much more content. Look at the highly ranked hubs, by highly ranked hubbers and observer their length and compositions.
A hub never has to be "finished". You can start with a short hub, and then keep coming back to add more content (text) capsules, and experiment with other capsules, like news, polls, etc. You'll find that as your hubs grow in content and quality, your readership and revenue will also likely increase.
You can also change directions with a hub, as you reflect on it and research the topic for yourself.