I don't necessarily think that steem power as a linear value alone has to be the only way to calculate vote worth, but I do think it has to be at the core.
For example, another system that MIGHT work is using a pagerank type setup where everyone declares trustworthy users, and essentially a web of trust forms. Then, the power of a users vote also is rated based on the value of people who trust them. This is still open to sybil attacks, however people can choose not to trust (or even distrust) people who are clearly only trusting their sockpuppets.
Sometimes I wonder, only sometimes, mind, what would happen if voters wouldn't get curation rewards at all, and the only way of making something would be posting content and get votes. I only think about that because I would like to see an end to all the gaming and bot voting for money and sock puppets and other shit going on troubling the waters. I must admit I haven't had any coffee yet.
These are the questions that are worth asking, but you have to think like an adversary in order to determine the viability. :)
One important aspect of curation rewards is that it is economically incentivized to vote for a post that will be voted on by other people. The reward for doing this is greater than the reward for you creating a post of your own and using that vote on your own post instead. For example, say, I could upvote my own comment and earn 5 cents... or I could use that vote to curate and earn maybe 10 cents.
If there wasn't curation rewards, one would be economically incentivized to only use their voting power on their own posts. Why should I upvote someone and earn 0, when I can still upvote my own comment and earn that 5 cents?
We're stuck between a rock and a hard place.
Unless .. you have a population that votes because they actually like something in stead of one that votes for making curation rewards. There are other motivations for voting than just the economic ones. No idea how it would play out in practice, though, so feel free to call me naive 8-). I know I vote for things I like without considering curation rewards at all, and not just because I hardly get any anyway with 5000 SP.