I'm begging for a high-rep privilege to delete obsolete comments.
Things like "Hey, you forgot XYZ" -- "Oops, fixed; thanks" etc. I'm not talking about legitimate, information-rich comments not edited in to questions and/or answers.
As an alternative to straight reputation, perhaps a combination of moderator-eligible and reputation.
Q/A editing comes at 2K reputation. I'd argue Q/A editing can cause more mayhem than deleting clearly-irrelevant comments, although as has been pointed out, there's a visible audit trail.
I think the combination of a reputation far above "Trusted User" and moderator eligibility hits a "sweet spot" of users that are both heavily invested in site upkeep/maintenance, and have the ability and motivation to take on this relatively low-level maintenance work.
This would help clean up some Q/A noise, and off-load a small amount of work from the mods, and, I believe, increase overall quality of Q/As.
- Show deleted comments and who deleted them to the author, trusted users, and mods.
- Let mods and trusted users undelete comments.
I feel this is a reasonable approach, when combined with rather high rep reqs and moderator eligibility.