Well I know the APR from staking sps is around 50%, but I don't believe that takes into consideration vouchers. I also don't think that providing LP with SPS yields vouchers.

There is definitely math to be done. I'm not sure what the voucher price would need to be at to make staking SPS the most profitable option. I imagine all options tend to move toward a baseline profitability. If providing LP for instance gave 2x more rewards than raw staking, people can just dump their daily airdrop to buy vouchers for instance, or just compound their position for increased upside.

As complex equations are a little out of my grasp, I can only give answers that raise more questions.