BTC price will be around 800 - 1200 USD this year, high price means that BTC mining is more profitable. So it is also the right time to sale some spare BTC.
What is "spare BTC"? I think there is no such thing. All the fractions of BTC we have are not spare for us. We love then and we cherish them.
No one wants to sell them unless we are in a desperate need of fiat money.