Yeah but it's anonymous / via bitcoin, no one could stop you from doing a 1000 'small' donations under a 1000 different identities, yet you control them all?
I could even imagine automatically refunding the fee for those casting losing votes to avoid wars of attrition... I guess that's essentially an auction.
Anonymity on the internet pretty much inherently means that you can't tell how many actual individuals a given set of apparent individuals really are. You can tell how much money they have (or CPU power, bandwidth, or various other proxies for wealth), but that's about it. I don't see how this wouldn't be an inherent problem for any cryptocurrency (or crypto-whathaveyou-system) attempting to force decentralization (see; the primary actors in Bitcoin split war.)