Aegis are expensive and require more screening vessels, not that it wouldn't be greatly beneficial, but we also have need of more anti-sub ships/subs to counter the ChiCom threat. Plus, would need more LCC's (command ships). The budget only allows so much, I'd have to look at Cain's plan in more detail. I think the ChiCom threat could be checked relatively inexpensively...but an extended naval shield of global dimensions is a really big deal.