Sell enough on a regular basis to offset any costs, such as electrical at least this way you are not going to lose anything, think of it as your are buying the ETH with your slightly higher power bill. Of course seeing you are only mining 0.5 ETH a day, I am guessing you are mining with one or two GPUs at roughly 25-30 MH/s hash-rate, so this might not be that much extra cost to your normal power bill.
Hold on to the rest for times when you think it is peaking and sell then. Right now it is low and I think we will see 0.03 again sometime soon. A nice piece covering Ethereum was published today at the NY Times so I think this will help to reverse the recent downtrend, even if temporarily. My point is to hold out for the peaks to sell and don't get scared off by the lows.