Have separate maker/taker fees. 0.5% is fairly high. Change to 0.2%/0.4% maker/taker. Or lower.
Most exchanges charge lower fees for limit orders that add liquidity to the order book. Bitmex even gives a 0.25% rebate for limit orders, instead of charging a fee. I understand that Vaultoro provides a unique service so higher fees are justified, but 0.5% is pretty high.
I definitely suggest changing to some form of maker/taker fee model, where the maker pays half the fee of the taker. So 0.2%/0.4%, 0.15%/0.3%, etc.
This will add liquidity and encourage more transactions, as fees would be lower overall.