Should I skip ECC RAM for a weekly cold storage server?

Yes, it’s probably a waste of money. ECC RAM protects against bit flips during constant memory operations, but your cold storage box runs only a few hours weekly, making the risk vanishingly small. The 20-50% cost premium is better spent on higher-quality drives, more capacity, or offsite backups—things that actually protect against drive failure and disk bit rot. For a homelab or personal backup server, you’re fine without it.