The way you get people to spend their coins is to increase the price of the coin or to give them incentives to spend. PoI in a way is a lot like those reward points you see in credit cards / debit cards and people love that stuff.
I respectfully disagree. Increasing the price of the coin encourages people to hoard, not spend. If people think time will increase their wealth, they will not spend. That is why deflation is such a threat. In deflationary economies, spending power increases over time, and consumer spending drops precipitously.
Inflation has the opposite effect. It erodes spending power over time. While it's bad for an individual, it's healthy for an economy. It makes people less likely to save and more likely to spend because it causes spending power to decrease over time.