I don't like this idea, but it would be interesting if the tax we're talking about is sales tax. Everyone would get some votes and there would be financial incentives for millionaires to actually spend their money and juice the economy so that they could have more votes.
Should we not give those who invest in the economy, and presumably in job creation preferential treatment over those who purchase yachts, airplanes, race cars, and other consumption goods?
Basically sales tax is the best way to know that your dollar is doing something of value.
If you look at the systems which recent advances have allowed humans to produce, you can easily see that the most valuable and desirable goods require highly integrated sub-assemblies and components, and the end products have high part counts. Your cellphone or computer alone is made up of hundreds or thousands of components, each requiring highly complex R&D and production, your car has 10k parts, an airplane 500k parts, and a space shuttle has 2000k parts. As a result, creating modern goods requires an ever-increasing number of 'steps', which in turn requires ever-increasing capital investment in R&D and production. We should be encouraging this investment if we want to continue to make more advanced and complex products available to everyone (including consumers).
The point is it's easier to figure out what you're contributing to the economy via sales tax than it is via investment. It's difficult to tell the difference between the guy who has invested $2 billion in 10,000 different startups, and the guy who is generating no revenue sitting on $2 billion in non-productive land in the middle of nowhere. Clearly we don't want to tax investment in startups just so we can see who's investing.