Bang on assessment. Our lack of funds is a major problem.
An air force is absolutely critical DCA, OCA, CAS and interdiction, but then for really long-ranged strikes we need a decent stockpile of missiles too because our air force can't reliably extend that far. Also it's a fall back in the event the air force is overwhelmed in other tasks, or god forbid destroyed. This makes the underground missile cities attractive as a dual strategy alongside a powerful air force.
But the amount of money needed to invest in both simultaneously is huge.
Also the underground base can on a smaller scale like the Chinese one can prevent Iran-style decapitation strikes that totally disrupt/eliminate your C&C structure.