As for stations, these mirror the designs of the at-grade stations on the system, so "consistency" was likely a large influence. San Diego also runs more conservative for a large city, so cost savings are a big talking point amongst politicians.

If cost savings arwbwhat they were aiming at, they could drop a couple of P&R facilities or the redundant elevators. And the choice of a viaduct in many areas is definitely primarily to not inconvenience car traffic