“We’re looking at a home on over a quarter acre, most of it is on a hillside and unusable. The agent we’re working with keeps telling us that the huge lot means the property is worth more. Is it?”
If the large lot means you have greater privacy, a view, can add an ADU (granny flat), or expand the home, etc., that can indeed add value.
But unusable sloped land in itself only inflates an owner’s ego, not the property’s value. In fact, it can sometimes be a small negative as you’ll likely have more land to maintain and clear to avoid a fire hazard.
I think your agent doesn’t know what he’s doing or he’s saying whatever he thinks will help make a sale. Neither of those are good.