Luck is usually seen as a Spectrum, ranging from Good luck, to Bad luck. With Good luck, you draw a Royal Flush, With bad luck, You Trip down an elevator Shaft. Either way though, Bad luck is not the Absence of Luck, it's just on the opposite side of the Spectrum from Good Luck.
So How does Storing Luck Work? We've never seen it used (Outside of MAG), But I don't think it's used in the Way people think it is. as in, storing give you bad luck, tapping gives you good luck. Realistically, (Yes, I'm using the Word Realistically while discussing Magic) Storing Luck should put in the Middle of the Spectrum. Pure chance, and Luck no longer affects you. When you're tapping Luck, you get both Extremes, You always either get Royal flush, or Uno cards.
Then there are people who are 'Born' Lucky Or unlucky. If these people store Luck, Do they store Bad luck or Good luck? or just Luck in general? Would they multiply their base luck, or The Absolute Value of their Base luck? Personally, I think they Store their Base luck, so a normally unlucky person would be better off by Constantly Storing than by Tapping.