Start with what a failure would cost
Rank each asset by the damage its loss would do, and by how long you would be down before it is back. The ones that score high on both are where hardening earns its keep. Building age barely enters into it. A forty-year-old structure standing between a threat and a critical load can be worth more hardened than a newer building that was never exposed in the first place.
Hardening is the option owners skip too fast
Owners tend to jump from preserve straight to replace and lose the middle option entirely. Hardening keeps the building you already paid for and closes the specific gaps an assessment turns up, without gutting the place to do it. It only pays off when it is built to a real threat basis instead of a vague wish for something sturdier, and when the work can happen around an occupied site. On cost and embodied carbon, it usually wins.
When hardening is the answer, the protection has to be specified to a defined threat basis.