You realise you can always still restore that backup onto someone else's server? When you need to restore from backup either way. I don't really see why one would pre-emptively pay for it
> If I accidentally lock myself out, there's no serial terminal to fall back on.
Why not? That sounds like a choice you can make. The hardware I hosted on either had a KVM built in or can just attach a USB keyboard and VGA (or nowadays HDMI) display
Power outages aren't common in my area, and otherwise a UPS is not that expensive (compared to if you pay a third party to set up redundant power for your hobby system)
You can choose to pre-emptively pay the cloud premium and give them access to your server so you can also social engineer yourself back in via customer support (after all, if you aren't expecting to lose the password and thus don't need to convince a human to let you into your hosting account, then you could also hold onto your own server's password). It just all seems very opposed from the self-hosting spirit where you're self-reliant, which apparently you value since you were considering whether to self host?