Luck in the duck comics is a bit of a theme, huh- I’m not sure I have opinions that can’t be overturned by good story writing/unusual situations, but my general understanding of it is there’s a sort of scale that the ducks abide to and which can, in turn, affect the story and how they come out of it. Donald’s luck is probably a little more in the orange than I’ve drawn it here to be honest, and this is all without the important factor of fairness- 

I’ve explored it before, but the fun thing about Gladstone and Donald going up against each other is that even though Donald’s luck is bad, if he plays fair and tries hard, then even if Gladstone ‘wins’ the contest or race or prize something always happens that makes it clear that Donald actually is better off without it, and has more valuable treasures in life already. Gladstone’s luck isn’t infallible, either, and if he tries too hard to use it, or uses it badly/for something that he doesn’t deserve, it can go completely against him. I also see him as being genuinely afraid of cursed objects, which would imply that a heavily cursed status is even stronger than his latent Triple Distelfink luck.

In terms of luck ‘cancelling out’ I would say rather than hitting an average point (e.g. Gladstones luck meeting Magica’s luck would equate to low level good luck), it is more interesting and probable that each type of luck would be active, but somehow have to compensate for the other. There’s a story where Donald gets hold of Gladstone’s gold four leaf clover (which would count as ‘augmented’ for him), and it results in everything going horribly wrong like usual… but ends up with the situation fixing itself in an equally dramatic way. He ends up returning the clover because it’s too much stress having to deal with both kinds of luck at once!