So it's basically a quick measure to see if someone is here to contribute or exploit, with the caveat that it doesn't account for people who need to power down for unexpected expenses and other situational effects.
What if you added a modifier for account age and post count? If someone was active for 3 years, powered down 6 months ago, and returned to powering up, that should mean something different from someone who started posting last month and is frantically powering down every HP they earn to send it to an exchange.
All these measures that you suggest are there in the data. Yes they can be investigated and added as a metric/plot/dimension