My first acoustic, a $100 Fender from the year 2000, has spent precisely zero minutes in a case or with a humidifier. No issues related to humidity. Never was a great guitar so I'm comfortable letting it dry out. Mostly it lived in Oklahoma, a humid state, and then the last few years in Colorado, a dry state.
My second acoustic, a $150 Stratacoustic from the year 2009, is the same.
Come to think of it, I simply don't keep stringed instrument in cases. Wind instruments, yes, as the pads dry out. But guitars and basses, nah. It's your call though. If you'd be heartbroken if it become unuseable and unrepairable, I guess try to control the humidity somewhat.