But is inflation needed? Why can't we just keep the currency at the same value?
The government will not want their foreign reserve to deplete and finish. That is why they will prefer to manipulate and devalue their own local currency. And why does it only happen to money? For example, the same wouldn't happen if we used gold as a currency instead.
It can not affect gold because the government do not have control over gold price.Is inflation a ploy that the government uses so people don't get rich off of savings?
Yes, people should know that fiat do not have value. The value in fiat is when you use it for something like business or investment. 
