It's not a question of a software bug--the DATA on the volume was indeed corrupted (Invalid Node Structure) and the software reported that. It happens: sometimes corrupted data can be fixed in place, but sometimes you just have to rely on your backup (which I do have).
But has there been permanent PHYSICAL damage? That's what's unclear to me.
I could replace the drive just be safe, but I'd hate to do so needlessly. (It would mean being without my computer for a while.) I'd prefer to do some kind of further testing and have a better idea. (Or maybe that "speed inhibited" message always means physical damage? But I WAS able to read all data from the drive even after the error--just to make one extra backup. I just couldn't write or boot with it unless I reformatted.)
The way I read the error messages you mentioned, it looked like the logical (data) damage could've been the result of some sort of physical? drive issue. Even if there was filesystem damage, DiskWarrior would normally not say the drive was being difficult (my paraphrasing here).
If you feel the hassle of pre-emptively replacing the drive outweights the hassle of replacing it when it fails at some point, then the solution is simple enough: continue using the hard drive while ensuring you continue to have good backups so that when the time comes, it's just a swap and another restore.
It's really a judgement call. We don't yet have enough information to be completely confident.
You're not seeing, feeling, or hearing unusual vibration or loud clicking due to something other than parking or unparking, and the drive is still operable. So that suggests the drive ball bearing is OK, interface electronics is OK, power supply is OK, r/w head, arm, motor is OK. It's not clear if there is any media degradation issues or not -- that would require a more in-depth test of the drive plus any analysis of drive's reported SMART data.
In other words, most of the major parts of the drive sounds OK but still not known if you have a failing drive or not. Best bet here might be to do a full backup then a full read/write (destructive) scan of the HD while booted off the DiskWarrior CD and then restore the HD afterwards.