In that case, I will actually need to read some non-Narnian Lewis. It'll be interesting to see if anybody here has read Out of the Silent Planet or anything else.
As for Narnia; I'm not really sure a direct comparison can be made between Narnia and Midde-Earth. The former was aimed specifically at younger children, the latter at, to generalise a little, the oddballs in society.
But more importantly than that is the religious message behind Narnia. Narnia is accepted as a rewriting of the Bible, more or less. That makes Peter and co. divinely appointed rulers rather than dictators. And - though Medieval kings may have claimed this - the difference here is that the children were appointed as rulers directly by Aslan. Their rule is a theocratic one.
However, they are benevolent dictators. In this respect, Lewis doesn't differ from Tolkien. As Elessar rules in name but gives regions a lot of autonomy, so the Children rule in name but, I presume, let the inhabitants of Narnia go about their business. Certainly we see no Big Government, whether dictatorial or communistic, but an appreciation of individuality.
So, by my method of rambling about the first thing to come to mind, I have determined that their political views were more or less that same. Which means the difference is not in terms of political outlook or stance on authority, but in rewards.