It's not really a use other than Staking but many of the Competitive Events have an SPS requirement in order to compete. So if you meet the staking requirements go ahead and join an Event or two (just be prepared for stiff competition).

Other than that I hear they are going to be used in the upcoming land expansion. Also if you don't want to stake them you can add them to the SPS:DEC liquidity pool in order to increase your SPS airdrop rewards.