re: You wouldn't need nukes or asteriod strikes.
The nukes or asteroid were for the Sahara to create a basin. Doing something like that would be very risky and a task for a future generation with better knowledge and technology then we posses.
We certainly have the capability to build a tunnel to Death Valley, but the cost would be high. Perhaps making the real estate around the new sea more valuable might make it worth the cost.
The evaporation around the new sea should cause more rainfall along the neighboring mountains and that would be another plus.
I wonder if another benefit would be lubricating the faults in that area so the quake dangers drop?