I've been playing Open Legend RPG and I love that the Advantage in that game can be stacked. I love it when players try to strategize and stack as much advantage as possible.
I want to do this in D&D, but triple advantage doesn't really differ much from normal advantage. So, I was thinking of giving a +1 modifier for advantage instead of a double roll. This way players can stack +1 for every clever thing they do.
Will this work or will this throw D&D off balance? Any idea?
PS. Disadvantage could stack as well with -1s.
This is going to be difficult to balance
Having advantage on a roll is roughly equal to having +5 to your roll, and having disadvantage is roughly equal to having -5 on your roll, as suggested by applying advantage and disadvantage to passive checks.
Your suggested change would require somebody to have 5 different sources of advantage to get the same bonus as they do now, which seems extremely difficult to get unless you start also house-ruling a lot of ways to get advantage.
And once you start houseruling a lot of ways to get advantage, to try and make up for advantage now being weaker, you're making special abilities that only work when you have advantage a lot stronger.
By changing just this one thing, you're very likely going to have to make a lot of extra changes that will break other parts of the balance.
Some things that come to mind that you might break: