Firstly, try contacting [email protected] detailing what you'd like to build and see if they're interested / able to collaborate or provide you the necessary access / APIs.
I'm not a programmer by any stretch of the imagination, but have contacted the mods from time to time and found them eminently approachable.
Secondly, if you can't see the up or down vote buttons, try clicking on a comment or submissions time stamp immediately after the username. For reasons I don't know sometimes the vote buttons aren't displayed in the regular view.
One of the things I super appreciate about HN is the (almost) complete abcense of feature creep.
I don't think this is a feature creep, I think it's useful. Otherwise I'm going to have to code something to scrape through HN for me and provide that additional context, and even then I still would be missing a way to filter down on HN comment data vs my own local db of upvoted materials.
Mostly the favorites feature is used by me when I cant upvote something since thats what HN defaults to. I would use it more often if I could filter by my own saved content.