No, it's not a dumb question. When I started here, I also thought that.
No, your Hive balance does not change when you upvote some post.
Hive has a certain inflation (currently around 8% as far as I know, and this percentage decreases from year to year). This year this inflation corresponds to 26.2 million Hive. And this money is distributed to author rewards, curation rewards and interest for HP holders.
The more HP I hold, the more value my upvotes have.