The bridge is at risk from a big subduction zone earthquake. Secondly, it's not a matter of if, but when such a subduction earthquake will occur, most recent studies done by DOGAMI and other regional geologists suggest a 40% to 50% of that happening in the next 50 to 100 years for a magnitude 9+ earthquake. If that happens the I-5 bridge is probably going to fail.
So yes, we need a new bridge to account for that, and they probably need to build in the capacity for light rail, as projections for the next fifty years suggest Clark County will continue to grow putting an even bigger burden on existing transportation infrastructure.
Build it with bonds and available federal transportation funds, repay it with tolls (on it and the I-205 bridge with discounted monthly commuter rates for people who have to go back and forth every day) and pay the thing off in 20 or 30 years via the people who use it.
It worked just fine in the bay area and it will work just fine here.