I think the level up reward could be an interesting idea, though it may need to be carefully balanced, I guess. It could give some more variety to the lairs system, which I think it's always good. As it would be a really good advantage, maybe it could only be on the higher-end lairs (Wights and Dragons, not sure if I would count Trolls because with Pikes they are not difficult to bring down), so the higher the risk is, the higher the reward becomes.
As for the river and mountain ideas, maybe that'd be good for map-specific stuff, but I'm not sure if something like that would work in the common gameplay.