For system failure, yes, but not if data retention and recovery is your primary concern.

When building a device primarily used for storing personal things, I'd much prefer to save money on the motherboard and risk that failing than skimping on the drives themselves

You actually want reliable MB & RAM to ensure data doesn't get corrupted in memory first. Since you have various ways of writing data to disks that offer you resiliency.

Eh, cheap motherboards aren't a panacea that can't hurt the rest of the hardware, I personally don't skimp on motherboards, and would much rather skimp on the drives themselves as I have redundancy and 1-2 drives failing wouldn't hurt too much. And data retention is my top priority.

Motherboards have fried connected hardware before, poor grounding/ESD protections, firmware bugs together with aggressive power management, wiring weirdness and power related faults have broken people's drives before.

What I've never heard about is a drive breaking something else in a system, but broken motherboards have taken friends with them more than once.