Instead of saying only people who 'understand politics and care about it should get a vote/get greater voting power' why don't we focus on why people don't have this information or hold such an attitude in the first place?
A lot of people are apathetic as a result of not having learned what it means to be a member of 'civil society' or more generally a democracy. Add to that, many have very little understanding of what politics really means and how it impacts on the individual. People are also socialised into apathetic families...
Yeah, ok some people donkey vote. Some people vote only because they have to and end up voting based on some irrational judgment there and then. But I would say the majority of people (aged above 30) vote based on a criteria they see fit; whether it be through analysis of policy or an inclination towards Piers Akerman.
Not all people are highly educated, political, moral beings and they're opinion has just as much validity as the white collared skilled professional. To say one is better than the other is to suggest there are not solely 'misinformed'/'underinformed' people out there, but there is a 'wrong' and 'right' way to live your life.
Also, preferencing one demographic over another would be disastrous. Imagine if corporate business execs had greater voting power than the rest of us? political campaigns would be overhwhelmingly aimed at them, and policies skewed towards the elite (or perhaps this is already happening? coughliberalpartycough)
Although, maybe if the poor had greater voting leverage politicians would start making homelessness a more important issue... and lower tax on booze
The point is, most people ultimately have a rather parochial agenda when voting. And everyone has the right to stipulate what they think is right for themselves regardless of who they are and what they know. After all; they don't implement plans. They just exercise their opinion and attitudes.
When the state starts telling you that 'they know best' and that 'experts know best' then liberal society is d00med.