Just remember to always include a link back to the original source article so everyone can get involved and see the rest of the conversation.
Every blog targets different people. We come to the hobby for different reasons, be they competition, gaming, socializing, the art, modding, creating, etc... Each of us have a different mix of passions. The people reading your blog might not be reading another blog that you follow. This is because blogs usually stick to a certain style or certain topics - but we all deviate from that now and then. I don't follow gaming related blogs, but occasionally I find gold on them through links on other blogs I follow, or through Twitter.
I make a point of sharing links in my Weekly Update and through Twitter, because I think it's important to share these things with everyone. When I find something I think my readers might find interesting, I share it. If you're talking about something through the comments on another blog, why not share those things too?
Consolidation and Editing
By consolidating a number of your own comments, you can organize your thoughts. In a thread, and as we speak, our opinions shift, we (in theory) enter into a discussion where we're open to new ideas and our minds can change. We also might repeat ourselves throughout the thread(s), so this is an opportunity to take a bunch of our thoughts and clean them up. I always recommend rereading any post you write numerous times anyway, preferably over the course of a couple days - so editing yourself should be nothing new.
Once we have our thoughts consolidated, we can continue the topic of the original post on our blogs. Perhaps you've got some more ideas that you'd like to share, or the ideas change and evolve as you're editing them. Comments themselves can make up the bulk of an article, but there's nothing stopping you from expanding on them and possibly turning them into something more. (Inspiration for a blog-fu post, for example)
Sharing and Replying to Comments
Instead of just continuing your own thoughts, you can address some of the issues that other people raise. Now, this might not always work too well, because the people in question might not be following your blog. In the interest of sharing information, the things that others have to say are still valid and it's worth including the thoughts of others. If you think they add something, quote other people AND give them credit. You can then respond to them.
How often do you return to a blog you've left a comment on, in order to read the responses that follow? Do you check back after a few days, or only on the original date you read it? I'm actually curious about this. When I comment on something, I usually create a shortcut to the article on my desktop. That allows me to followup and read what others have to say and not lose the original article or forget about a conversation.
We all follow a lot of blogs, and for those of us who also write for our own and possibly a few more, time can become a factor. I enjoy sharing with the community and having discussions with them, but I've also had to find ways to cut back as well. I don't want to reach a point where I'm considering not commenting on something I find interesting because I've still got some blog post to write.
Personally, I want to be able to share stuff with all of you, but my life's been upside down recently and it hasn't allowed me much hobby time. I still find time to kick my feet up or take a break and read through blogs to relax. (Otherwise, I'd go crazy) Reusing comments helps to allow me to do just that.
Beating a Dead Horse
You should also be aware that you can run into a problem with this strategy if the blogs you're sharing comments from are ones that are followed by many people. If people have already read the topic and talked it to death, they're not interested in talking about it again on your blog. This is more useful if you think your blog might be followed by a different group of people.
I also don't suggest posting these sorts of posts regarding topics that are heated. If a huge flame-ware erupted on the original blog / forum, then you're just asking for another argument on yours. Don't fuel angry fires, let them burn out and move on. Remember, any post you feel strongly about should sit for a few days before you post it, so you have a chance to cool down and edit.