I think this fits in with the difficult issue of defining merit. It would be very difficult to say who has the relevant knowledge to be permitted to vote on certain issues. Lets take Education for an example. Who would get to vote on educational matters? Teachers surely. Policy makers. Those with degrees/qualifications in education? What about social sciences in general? That seems to make sense to me. But then what about parents? Shouldn’t they have some say in their child’s education? But everyone has been to school, if they’ve experienced it then aren’t they in a position to formulate a useful opinion on what could change? Then that pretty much includes everyone… If we say that age is a bad way to decide who votes - then pupils? Could we argue they have some say in their own education? I think that would be pushing it a little, most would try and hold a no homework vote!
My point is where do you draw the line in who has expertise in a field? or who is sufficiently effected by a certain aspect that they deserve a right to vote on it? As every aspect of society is interlinked, the people who it would be argued deserve to vote would be constantly expanding until it included everyone anyway. But then you have the 100 idiots problem again.
Unless you have set ways of defining and measuring merit and strictly impose voting rules based on this - but then there is the very difficult issue of how you define merit, who defines merit etc.
I think a better way (without totally throwing away the idea of merit/expertise based voting in certain fields) would be to focus effort on reforming and improving the education system itself so that the people coming out of school at whatever age are sufficiently balanced, intelligent, socially aware etc. so that their vote IS an educated one. Instead of trying to find a moral way of cutting out the 100 idiots - help them not be idiots. There will always be some, but they needn’t be the majority.