I think it's a very pertinent question and I think you need to be realistic about the time it would take to outreach to the webmasters about your comments and then how likely they are to be removed.
The answer to me would be "a long time" and "not very likely" - which would essentially be a waste of time considering that you could be building better links during that period.
It might make you feel a bit uncomfortable, but I'd ignore them until you get an unnatural links message - at which point, I'd outreach and get ready to disavow (so you could make a note of which comments you think might trigger this, those on unrelated sites with a lot of outbound links for instance). Until then, I'd spend your time more wisely by optimising your site and building better links. There is also evidence to suggest that Google might be going down the route of devaluing links on the fly, which may happen to you in the future (or may have already happens). Should it occur and you see a rankings drop (but nothing too serious and no link warning message), it's important to have a number of high quality links built or ready to be built to replace those links devalued.
That's where I'd spend my time.
