Well if you treat it like a continuous function, then yes of course it would drain away the voting power. My calculations assume over the course of the day. So n could be at 100% and n + 1 would be x seconds later and also at 100%. Or more precisely, using the (555 * .02 * .02 * .9 = 20%), n is at 90%, but n + 1 is 156 seconds later and also at 90%. You could vote give a 2% upvote at 90% voting power every 156 seconds and every upvote would have the same value (and thereby capture the equivalent of a 10 full upvotes every day, because (10 * .02 * 1 = 555 * .02 * .02 * .9).

Now, obviously there would be some random distribution in the actual voting power, as purchase transactions are randomly distributed throughout the day, and sometimes the vote is at higher or lower power. But if the amount voted is correctly adjusted to always deliver a consistent return, then the value paid for an upvote would always be a function of the maximum upvote value. There would be high and low payout days, but over time the distribution would approach uniform and the value captured would be close to the value of 10 full upvotes daily.