And the "it makes your vote more powerful" can absolutely not be abandoned. I hear lots of small holders complaining about how those who hold more SP have too much influence and that something should be done (and various ideas have been proposed and even tried) to make voting power more equitable. I believe that would be a mistake. Investors do need to be rewarded, and @heretickitten is right in that there needs to be even more reason to buy in than the upvote value. However in the mean time, it is absolutely vital that the upvote value not be curtailed in any way. If you own lots of Steem Power you should be free to upvote whatever you want at whatever strength you want.
With that said, there then also needs to be plenty of marketing to attract new big investors so that there are more of them, and in this way reward distribution will organically get spread out to a wider variety of authors and content.
Steem Power has to be valuable to both small and large stakeholders alike if it's going to take off. The system won't work if power is forever held by a small few, and there's no value in buying small amounts of Steem Power when someone who owns 100 times as much Steem Power than you, gets 10,000 times as much voting influence. In the end the larger stakeholders will be better off with higher valued Steem than more a larger vote in a smaller pool.
I could go with a more linear incentive plan, if that is the problem. In fact, it would be much more fun for me to acquire more SP if I could see a corresponding linear increase in the monetary value of my upvote, so I'm not protesting that. What I don't like is for the whales (or more accurately, those authors they choose to upvote) to be punished or curtailed for using full or nearly full voting power. Eventually I'd like to be a whale. And I want to be able to vote full strength whenever I want.
Yes, I agree with you there.