I am not for a bonus because of high ground, as it makes no sense in my opinion. But if Larian goes for a bonus, then of course I would prefer +1/+2 over the advantage/disadvantage system we have now.
The best solution would be a cover system, but we will not get it, I am afraid.
For spells: an increased range does not make sense, in my opinion. If we get a bonus, spells that use a ranged attack roll (e.g. ray of frost) will use that at well. But that leaves the question, what do spells get that have a saving throw mechanic? If my wizard casts e.g. Fireball, should there be bonus on spell save DC as well? For me it makes not much sense, but for balance reasons, there should be something like that.