An upvote/upmod is also called a "save." If you look in your profile, you can see all of the submissions you have upmodded under "saved stories." There have been a couple times where I glance at a story, know it's interesting and something I want to read later, and upmod it to save it for later.
It's not an unnecessary upvote—I thought I made it clear that this behavior was part of the site's design. I rarely upvote stories at all, so stories which were compelling enough in the first couple of paragraphs to cause me to want to read them later are worthy of an upvote, in my eyes.
I think a much more disturbing trend is rush-upvoting everything that comes out of e.g. TechCrunch.
I save the HN post itself, not the endlink. It's better in case you want to comment rather than go straight to the article. And since you saved the HN link, you can always easily navigate to the article later. I don't read in instapaper itself, I go direct to link. Instapaper is just a really efficient bookmarking tool for me.
