What benefits do high ground currently give? I see that attack rolls were mentioned, which logically make some sense, but mechanically would suck in a game.

If anything it should increase line of sight and give a small buff to range, but it shouldn't give a better chance to hit and damage. It's not a Wasteland-type game where cover is necessity.

Maximuuus also makes a good point in that simply being safer for a round or so from melee is a good bonus in itself. I know I stacked my range uptop at the Goblin camp and placed a tank and melee at the top of the ladder. The safety to slowly pick everyone off is a good enough bonus.