Certainly Vetinari's been an exceedingly lucid and sane lunatic all along as he's behaved like a traditional and highly successful despot for most of the Discworld timeline I believe :twisted: And totally true to charactisation since we first saw him in Sourcery (when Coin turned him into a lizard?
) Also Terry says that he's been the Patrician since CoM complete with the candied echinoderms so he's
always been on the eccentric side
It's Discworld so he's had to be a political juggler and, because he's in an elevated position, he's always bent and reinvented the rules to his own ends (using the rats to escape from his own dungeon, keeping Leonard of Quirm in 'safe' custody, making Vimes go on leave in Thud etc) so I find it very hard to think of him of being insane at all, most especially in his treatment and constant manipulation of Moist who's the nearest thing to a peer for him (a human one anyway except perhaps the crossword lady) - but I haven't read Raising Steam yet so maybe there's something in it.
The point about him being from the middle classes though
Not likely I'd say. In Nightwatch when we see him at the Assassin's Guild still he's a little like Edward De'ath - impoverished gentry more and extremely intelligent and ruthless as a result, as a way to get back on top with the help of his 'auntie' with the highly dubious reputation from Genua. In Roundworld most aristocracy can trace their origins back to ambitious murderers, thieves and whores who were at the top of their game (or friends with the right successful thugs...
) so it's even more so on the Disc.
We are all rising apes who are not very noble on the way up remember!