It would be really nice, if we could define different discount levels depending on the shopping cart value in combination with one same discount code. This is a standard usecase for promotions.

Currently this is not possible, because you can only define one shopping cart rule per promotion.
Since you cannot create multiple promotions with the same discount code, multiple promotions with different shopping cart rules are not possible at this time.

Either it should be possible to create multiple promotions with the same discount code or there should be an option to apply customer-, shopping cart- and order rules for every discount created within a promotion.