This is indeed one highly instructive as well as entertaining thread, I've read through the conversations with gusto.
One aspect about the book that I find rather interesting (it has been delineated here) is the conflict between traditionalism and (betimes only ostensible) modernism. There are several fronts where this is germane, albeit with drastically different premises.
King Verence is of course desirous of gingerly modernizing Lancre. He's a crass contrast to the monarchs before him, trying not only to ameliorate the economic situation of his people (by e.g. enhancing the agriculture), he's also been shown to take the popular opinion into account when it comes to administrative decisions (e.g. he didn't enfore a new tax after one of those "spontaneous mobs"). The population of Lancre itself appears to be rather resistant to such measures, it's been stated numerous times that they do appreciate a sovereign at the head of the state for as long as (s)he doesn't intervene in the everyday life in an inordinate way. While Verence tries to be a trustee, a technocrat almost, the people in Lancre much more appreciate the traditional role
eo ipso as well as martial prowess (Jason Ogg is quite impressed by the Feegle-supported vim of his king, there are also a few mentions that Verence probably would've been a bit more accepted were he more coarse). Verence's unconditional will to be forthcoming and understanding is also the cause for the entire concatenation of events that transpire in this book since he invited the vampires in the first place.
Mightily Oats struggles between various sets of considerations regarding his religion. He's aware of the sordid history behind the Omnianism and the crimes that were executed in its name, but he also seeks more immediate, personal truths in his faith which are harder to extract the more he reads, thinks and reflects about things. While it does not fit into a civilized world to harass, proselyte or even prosecute dissenters/disbeliefers/members of heterodoxy, the underlying simplicity of such an absolute religion also brings comforting (as shallow as they may be) certainties with them. Count Magpyr even remarks in his disparagement that while the saints/"church fathers" of yore were insane, they at least had an unassailable faith. However, he also adds that he himself was responsible for some of the religious texts that were written many centuries ago, thus also putting Oats to the test (which is naturally in and of itself a typical biblical/religious theme).
Speaking of the Count, he certainly represents the most striking personification of said dichotomy between tradition and progress. He doesn't try to actively alter his nature whatsoever, yet he invests a lot of time and effort to sublime (as he sees it) that proclivity. He despises the vampiric customs of old, the haunted castles, romantic/heroized tryst between the eldritch lord and the eventually unfettered mob, the housekeeping by Igors etc. He does nonetheless still strive for the inherent power that comes along with the natural abilities of vampires, much more so, in fact. Instead of bluntly subjugating townspeople or raiding their houses at night, he contractualizes these matters in order to make them look legal as well as legitimate. He understands that by manipulating people's minds, he can much more efficiently gain power compared to applying sheer strength. Lastly, he tries to immunize his clan and himself against all the threats that ail his species, and rather impressively at that.
It's quite fascinating how all these conflicting priorities are resolved by the end. Oats apparently variegates (allusion intended) his faith into something that resembles pantheism, what with finding something holy everywhere he looks. He doesn't try to find a balance between written concepts, he creates a synthesis for himself. Verence/Lancre more or less continue with the status quo ante. The vampires suffer a crushing defeat on account of what could perhaps be described as narrative overstretch (modified from the theory of imperial overstretch). While classic vampires may not have been as dominant or astute as those influenced by the new school of thought, they did instinctively recognize the immanent balance of the tradition. The old vampires got killed again and again whenever their malfeasance grew too unbearable, but they probably never faced so many losses in such a short period of time.
On that note, I will concede that I'm not entirely content with how well things turned out in the end, though I have to admit that this is almost unresolvable. Carpe Jugulum's antagonists are fairly similar to those in Lords & Ladies: both the elves and the vampires can twist people's minds, turning them into abulic slaves. They likewise are comparable as far as their goals are concerned (the elves are plain sadistic and inflict pain for their pleasure, the vampires try to put up a veneer, but also regard humans as cattle or meat, especially Lacrimosa). The problem I have is that on top of the magic allurement (both antagonists share that trait), the vampires are also much more dangerous. Someone who can resist the glamour of the elves will find that these are rather pathetic creatures, whereas vampires are preternaturally strong, fast and bestowed with several talents (shapeshifting, flying, resistance to sundry pugnacious means; these vampires in particular are also resilient towards some of the tried and true methods of dealing with their kin). Considering that a deus ex machina was necessary to repel the elves in Lords & Ladies, I deem it rather improbable that beating the vampires with comparatively little casualties/effort would happen. There are quite a few convenient things that fall into place: the catastrophic consequences of imbibing Granny's blood (which also take full effect at the most fortunate time), the phoenix, the old Count... Now, Discworld novels were always more about the moral implications than the structure; as such, it is not unduly fraught with complications, but I did find it implausible to some extent. I really would've liked to see this set-up with a dénouement à la Steven Erikson (Malazan Book of the Fallen), i.e. a veritable clash between powerful forces (which would've needed some proper build-up, of course) since power invariably causes ripples and draws even more power (resulting in a convergence), this furthermore would've been an appropriate narrative ending, I think.
I sincerely hope I'm somewhat understandable, the bulkiness and clumsiness of many a sentence is palpable even to a maladroit perpetrator against the English language such as myself.