Having a higher fee for ZSA only makes sense if a ZSA transaction costs more to verify. Personally, I want a ZSA transaction to show as exactly the same as a ZEC on the ledger. The privacy benefit of such scheme itself will make Zcash more attractive than any other chains.
In a future where Zcash is the dominant chain, ZEC as a native currency will be valued differently than any other imported ledger including zBTC. To quote @balajis: