What I understood (somebody from Gridcoin community told me before) that it's not necessary to keep GRC wallet open.
But if it's better to keep it open - I'll do it.

Btw, it's interesting, how much your friends receive with several hundred GRC for staking?
Right now I have only around 15 GRC, but may be it's good idea to buy GRC on Bittrex and it might be good investment, if staking is profitable.