Are high PR comment pages without the nofollow tag valuable for link builders? Or does Google detect easy link posting like this and ignore it?
I think they could be valuable if the content on the blog post and its comments is related to your niche you could get very rich......as you have a product to find these
If they relevant and ontopic they can be a source of traffic too. If they have nofollow, yes they are valuable. Just don't overdo it.
if they are related to your site , it may help you. but dont forget google can detect the blog comment. it may also hurt your serp. you must be careful
another tip is to vary the link text, having the same linked text on each one is recipe for disaster or devaluing of the links. use different phrases and words. like the others say, I think "everything in moderation". google will be on the lookout for too much of anything. Have a few screen valid reciprocal links, a few good 'pillar' articles maybe for article exchanges, comment on good blogs, maybe get your blog listed in a few good directories......a little bit of everything.